Multiple heater control system with expandable modular functionality

ABSTRACT

A multiple heater control system includes cables, connectors, and junction boxes for user-friendly daisy chain connections of heater controllers and heaters in various configurations or combinations of individually controlled heater series and/or master and slave heater series. The heater controllers include process control of AC power to the heaters and upper-limit safety shutoff that is substantially independent from the process control. The heater controllers also have variable levels of control, adjustment, display, and communications functionality in a base module that is expandable to various levels with expansion modules that are attachable to and detachable from the base module. Connector, cable, and junction configurations, adapters, and latch features enhance user friendliness.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to power and control systems forheaters, for example, to apparatus and methods for powering andcontrolling multiple heaters used for heating pipes and other componentsin vacuum, process, delivery, transport, and other systems.

2. State of the Prior Art

Many vacuum, process, delivery, transport, and other systems used inindustry for conducting or moving various gaseous, liquid, or solidmaterials from one point to another include pipes of various lengths,sizes, and shapes that have to be heated to maintain the pipes and/ormaterials in the pipes within certain temperature ranges. Pipe heatersfor heating pipes for these and other purposes are well known to personsskilled in the art and have ranged from simple resistive wires and tapewrapped around the pipes to more sophisticated, insulated pipe heaters,such as those described in U.S. Pat. No. 5,714,738 (Hauschultz et al.),which is incorporated herein by reference, as well as many such heaterproducts that are available commercially.

Along with the development of pipe heaters for various pipe heatingapplications, there was also a need for better pipe heater controlsystems for regulating heat output from the heaters along lengths ofpipe and for monitoring and controlling such heater operations. Thereare many kinds and configurations of such heater control systems, suchas the ones described in U.S. Pat. No. 6,894,254 (Hauschultz), which isalso incorporated herein by reference. As good as such heater monitoringand control systems are, however, there are still problems that theyhave not solved.

For example, in higher temperature installations, the heat produced bythe pipe heaters can be conducted to heat controller components that aremounted directly on the pipe heaters, thereby potentially raising thetemperatures of such controller components to levels that can damage ordestroy them or that can corrupt or degrade data in logic circuits ormemories in the controller systems. Some power control systems are hardwired to heater components of the systems making it difficult to quicklyreplace them. Also, most industrial pipe heaters are equipped withthermal high limit fuses or thermal activated switches that cut thepower to pipe heaters if the temperature reaches a maximum temperaturethreshold, regardless of the cause, for the safety of personnel, toprevent damage to capital equipment, and for safety agencycertification. This function has been provided with a variety of thermallimit devices, none of which are entirely satisfactory for thisapplication.

For example, standard, commercially available thermal switches areinaccurate and unreliable due to their wide set point tolerances andcontact mechanisms, which can erode or, even worse, self-weld to aclosed position that renders them totally inoperative and can allow athermal runaway of the heater until either the heater element burns outor starts a fire. These problems are exacerbated when the thermalswitches are placed in or on the heaters where they need to be foraccurate response to the actual temperature of the heater and pipes,because the high heat at the heater is a major cause for suchdegradation of the thermal switches. Yet, the thermal switches cannot beplaced off or away from the heaters, because they would not be able torespond to actual temperatures of the heaters or pipes.

Thermal fuses are more dependable and available commercially, but oncethey expire, i.e., “blow” or “burn out”, they cannot be reset. Sincethermal fuses are typically embedded in the pipe heater structure nearthe heating element to be sure they are exposed to the heat near itssource, they are not accessible without destructive mutilation of theheater components and materials. Therefore, a blown or burned outthermal fuse renders the heater completely useless so it has to bereplaced. Also, thermal fuses age over time, and the higher thetemperatures to which they are exposed, the faster they age. Such agingoften causes thermal fuses to burn out at lower temperatures andeventually to burn out within the normal operating range of the pipeheaters, thus rendering the otherwise good pipe heaters unusable. Also,commercially available thermal fuses are bulky and difficult to installin pipe heaters.

There are sometimes circumstances that cause the temperatures of pipes,thus of the pipe heaters, to exceed such upper temperature limits thathave nothing to do with a runaway or uncontrollable heater. For example,it is not uncommon to purge or clean process chambers upstream from thepipe systems by sending high temperature gases or reactive chemicalsthrough them, which can cause the pipe temperature, thus also the pipeheater temperature, to temporarily exceed the upper temperature limitand thereby cause the thermal fuse to expire and open the power circuitto disable the heater. When the thermal fuse expires and cannot be resetor replaced, good heaters are ruined by such routine maintenance andother occurrences unrelated to the pipe heaters themselves.

Also, there is a need for more options and versatility in bothconnection and control configurations to accommodate a wider variety ofpiping configurations, applications, and user requirements. Each pipeinstallation is different and many operators need custom pipe heater andcontrol systems to accommodate their particular requirements, butdesigning and manufacturing custom pipe heater systems is expensive,time consuming, and often not feasible for most applications. Forexample, some operators want a control mechanism for each heater in aheated pipe system, whereas other operators prefer to avoid the cost ofindividual controls on each heater and instead use a strategy wherein asingle controller is used to operate an entire zone comprising a numberof individual heaters. Such “zoning” or “single point” control heatersystems often require complex wiring, which can create confusion andincreases the probability of wiring errors, or it can require customheaters to be designed and built to accommodate slaving and preventwiring error, which adds costs and complexity to the system.

Another example is that some operators require remote communicationswith heater controllers and remote heater system control capabilities sothat they can view operating status information and modify operatingparameters from a remote location, whereas others want to be able toview such operating status information and to modify operatingparameters locally at each heater within a system. Still others requireonly basic, pre-programmed control at each heater. Of course, there arealso operators who want any combination or all of these functions for agroup of heaters with only single point control.

These and other requirements in industrial and commercial use of pipeheaters creates a need for a more flexible system of pipe heatercontrols and wiring components that can be configured easily, neatly,and effectively to meet a wider variety of operator requirements.

BRIEF DESCRIPTION OF THE EXAMPLE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe specification, illustrate several example embodiments and/orcomponents that are presented to support the description, but not tolimit the scope of the claims in any way. In the drawings:

FIG. 1 is an isometric view of an example individual heater controlarrangement of the multiple heater control system;

FIG. 2 is an isometric view of some of the principal components utilizedin an individual heater control arrangement such as that illustrated inFIG. 1;

FIG. 3 is an isometric view of the principal components in FIG. 2, butfrom a different perspective to illustrate the connective components;

FIG. 4 is an isometric view of the individual heater control arrangementin FIG. 1 in its assembled condition;

FIG. 5 is an isometric view of an example arrangement of the multipleheater control system in which a single point heater control is used forcontrolling a gang or zone comprising a master heater and one or moreslave heaters;

FIG. 6 is an isometric view of some of the principal components utilizedin a single point control arrangement for a master and slave heatercombination such as that illustrated in FIG. 5;

FIG. 7 is an isometric view of the principal components in FIG. 6, butfrom a different perspective to illustrate the connective components;

FIG. 8 is an isometric view of the single point control apparatus forthe master and slave heater arrangement in FIG. 5 in its assembledcondition;

FIG. 9 is a cross-section view of a pipe heater mounted on a pipe foruse with either the individual heater control arrangement or the singlepoint control a master and slave heater arrangement of the multipleheater control system;

FIG. 10 is an isometric view of a T-type source power cable section;

FIG. 11 is a schematic circuit diagram of the T-type source power cablesection of FIG. 10;

FIG. 12 is an isometric view of a linear-type terminal source powercable section;

FIG. 13 is a schematic circuit diagram of the linear-type terminalsource power cable section of FIG. 12;

FIG. 14 is an isometric view of an example slave adapter cable;

FIG. 15 is a schematic circuit diagram of the slave adapter cable ofFIG. 14;

FIG. 16 is an isometric view of a T-type slave controlled power cablesection;

FIG. 17 is a schematic circuit diagram of the T-type slave controlledpower cable section of FIG. 16;

FIG. 18 is an isometric view of a linear-type terminal slave controlledpower cable section;

FIG. 19 is a schematic circuit diagram of the linear-type terminal slavecontrolled power cable section of FIG. 18;

FIG. 20 is an isometric view of an example basic heater controller withan enhanced control expansion module installed on the base module toprovide additional functionality to the heater controller;

FIG. 21 is an isometric view of the basic heater controller with theenhanced control expansion module in a position poised to be installedon the base module of the heater controller;

FIG. 22 is an isometric view of the enhanced control expansion modulefrom a different perspective to illustrate the example expansion modulecontact pad and light transmissive boss components, which are enlargedfor better definition of these features;

FIG. 23 is an isometric view of the basic heater controller with asubstitute dust cover poised in position to be installed on the heatercontroller base module;

FIG. 24 is an isometric view of the heater controller base module from adifferent perspective to illustrate a module mounting apparatus;

FIG. 25 is an isometric view of the heater controller base modulesimilar to FIG. 24, but with the mounting apparatus in a position poisedfor connection to the heater controller;

FIG. 26 is an isometric view of the mounting apparatus in FIGS. 24 and25, but from a different perspective to illustrate the operativeattachment components;

FIG. 27 is a schematic circuit diagram of an example multiple individualheater control configuration connected to an AC power source and to analert/alarm signal circuit located, for example, at a remote monitoringstation;

FIG. 28 is a schematic circuit diagram of the heater controller baseunit and the enhanced control expansion module connected to the T-typesource power cable and to multiple pipe heaters via a slave adaptercable, T-type slaved heater cable, and a terminal slave controlled powercable in an example single point control arrangement;

FIG. 29 is a schematic circuit diagram similar to FIG. 28, but with thecontroller connected to a terminal source power cable section;

FIG. 30 is a schematic circuit diagram of the heater controller baseunit with the enhanced control expansion module, the T-type source powercable, and the pipe heater components connected directly to the heatercontroller base unit as could be done for a single pipe heater or formultiple local control configurations such as those illustrated in FIGS.1-4;

FIG. 31 is a schematic circuit diagram similar to FIG. 30, but with thehigh voltage power and the low voltage signal circuit connected to thecontroller directly with a terminated controlled power cable toillustrate an individual heater control arrangement where the heater iseither the only heater or the last heater being controlled in a seriesof multiple, individually controlled heaters;

FIG. 32 is a logic flow diagram illustrating an example logic for theheater controller;

FIG. 33 is a schematic circuit diagram of an individual heater controlarrangement similar to FIG. 30, but illustrating an example high-limitcontrol circuit with a PTC thermistor temperature sensor;

FIG. 34 is a schematic circuit diagram similar to FIG. 33, but withanother example high-limit control circuit with a PTC thermistortemperature sensor;

FIG. 35 is an isometric view of a slave adapter junction box;

FIG. 36 is an isometric view of the slave adapter junction box of FIG.35, but from a different perspective;

FIG. 37 is a schematic circuit diagram of the slave adapter junction boxof FIGS. 35 and 36;

FIG. 38 is a schematic circuit diagram similar to FIG. 28, but with theslave adapter junction box of FIGS. 35-37 replacing the slave adaptercable illustrated in FIG. 28;

FIG. 39 is an isometric view of an example source power junction box;

FIG. 40 is an isometric view of the example source power junction box inFIG. 39, but from a different perspective;

FIG. 41 is a schematic circuit diagram of the source power junction boxin FIGS. 39 and 40;

FIG. 42 is an isometric view of a plurality of the heater controllers asthey are daisy chain connected with a plurality of the source powerjunction boxes of FIGS. 39 and 40;

FIG. 43 is an isometric view of another example variation of a sourcepower junction box with multiple trunk outlet connectors;

FIG. 44 is an isometric view of the source power junction box in FIG.43, but from a different perspective;

FIG. 45 is a schematic circuit diagram of the source power junction boxof FIGS. 43 and 44;

FIG. 46 is an isometric view of the controller base module and theexpansion module with the branch outlet connector of a T-type sourcepower cable poised for insertion into the inlet connector of thecontroller to illustrate a connector retainer feature comprising aresilient spring biasing tab;

FIG. 47 is a cross sectional view of the latch and resilient springbiasing tab for the branch outlet connector and controller inletconnector with the branch outlet connector plugged into the controllerinlet connector;

FIG. 48 is a cross-sectional view similar to FIG. 47, but showing thelatch lever pivoted against the bias force of the resilient springbiasing tab for release of the latch;

FIG. 49 is a cross-sectional view similar to FIG. 47, but showing a leafspring for providing the securing bias force;

FIG. 50 is a cross-sectional view similar to FIG. 47, but showing acoiled compression spring for providing the securing bias force; and

FIG. 51 is a cross-sectional view similar to FIG. 47, but showing aresilient compressible material for providing the security bias force.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

The multiple heater control system 10 illustrated generally in FIGS. 1and 5 is based on flexible and expandable modularity facilitated by theexample components so that various components and combinations ofcomponents of the system can be assembled and connected in a variety ofways to serve a variety of heater monitoring and control configurationneeds. The system 10 is best described in relation to two basicconfigurations—an individual local heater control configuration 12illustrated, for example, in FIG. 1, and a single point controlarrangement for multiple heaters in a zone or gang configuration 14illustrated for example in FIG. 5. Other combinations and variations ofthese basic heater control system configurations 12, 14 can be createdby using selected ones or all of the principal components of the system10, as will become apparent to persons skilled in the art as thedescription of these example embodiments and components continues.

The multiple heater control system 10 is designed primarily for pipeheaters 16, as illustrated in FIGS. 1 and 5, although it can be used forother kinds of heaters as well. Therefore, for convenience, thisdescription will proceed in the context of multiple pipe heaters 16 withthe understanding that it can apply to other kinds of heaters as well.

Referring primarily to FIG. 1 for the individual local heater controlconfiguration 12, a plurality of the pipe heaters 16 is shown. They aretypically arranged and aligned for mounting on a pipe (not shown inFIGS. 1-4, but illustrated in FIG. 9), as will be described in moredetail below. In this embodiment, there is a separate controller 20 foreach heater 16. Therefore, as illustrated in FIGS. 1-4, each controller20 is connected directly to each heater 16 in a manner that delivers andcontrols high voltage AC line (source) power to the heater element 32(FIG. 9) in the heater 16 as well as derives temperature informationfrom the temperature sensors 50, 52 (FIG. 9) in the respective heater 16to which the controller 20 is connected. Therefore, each controller 20responds to the temperature sensors 50, 52 in the individual heater 16to which it is connected and turns the high voltage power on and off tothat heater 16 according to settings in the controller 20, as will bedescribed in more detail below. Therefore, the high voltage AC powerdelivered to the heaters 16 by the controllers 20 is sometimes referredto herein as “controlled AC power,” whereas the high voltage AC powerthat is received by the controller from an AC power source, which issometimes referred to herein as “source AC power” or “AC source power”or just “source power”. The term “high voltage” in this context meansanything above thirty (30) volts. For example, typical heaters are oftenpowered by ordinary 110-120 volts, 220-240 volts, 440-480 volts, or anyother voltage that provides enough power to meet the heat productionrequirements of a particular installation. AC means alternating current,which can be 50 hertz, 60 hertz, or any other alternating currentfrequency that is used to power heating elements in heaters.

The plurality of controllers 20 in the individual local heater controlconfiguration 12 are daisy chain connected to the high voltage AC powersource 13 (FIG. 27), which can be associated with remote monitor and/orcontrol equipment 15 (FIG. 27) by the T-type source power/signal cables26, which contain both high voltage power lines for carrying source ACpower to the controllers 20 and low voltage signal lines, which comprisea low voltage temperature range alert signal that can be used for anypurpose and will be described in more detail below. The term “lowvoltage” in this description generally means any voltage that does notexceed 30 volts. Also, as indicated in FIGS. 1 and 4, any number ofadditional heater 16 and controller 20 assemblies can be daisy chainconnected together by additional T-type source power/signal cables 26and with a linear-type power/signal cable (not shown in FIGS. 1-4 butdescribed below) connected to the last controller 20 in the daisy chain.

Also, any combination of individually controlled heaters 16 and slaveheaters 16′ can be accommodated. For example, as indicated in FIGS. 5-8,additional individually controlled heaters 16 and/or additional singlepoint control zones of slave heaters 16′ can be connected to the T-typesource power cable 26.

For more detailed descriptions of example embodiments andimplementations, it is helpful to refer to the heater elements and totemperature sensors in example heaters, not for limitation, but to aidin understanding. In general, there are many varieties, materials, andstructures of heaters that can be controlled by these systems.Therefore, this invention is not limited to any particular heater orheater structure. However, to facilitate the description, an examplepipe heater 30 mounted on a pipe P is shown in cross-section in FIG. 9.This pipe heater 16 has many similarities to those described in U.S.Pat. Nos. 5,714,738 and 6,894,254, both of which are incorporated hereinby reference, but there are several different or additional featuresthat will also be described below.

In brief, the example pipe heater 16 in FIG. 9 comprises a high densitysilicon rubber heater mat 30 with a heating element 32 comprisingresistive wires or other resistive, heat producing material embedded init. The heating element 32 creates heat when an electric current flowsthrough it, usually at standard, high voltage levels, such as 110-120volts, 220-240 volts, or any other voltage level that provides enoughpower to create the heat needed for a particular application. The heatermat 30 is surrounded by a thermally insulating heater jacket 36comprised of low density, closed cell silicon rubber foam or any othersuitable insulating material. A fastening halter 36 with straps 38(FIGS. 1-8) can be provided to secure the heater 16 in place on the pipeP or on other components that are to be heated.

The heater 16 has a cavity 40 where high voltage power lines 42, 44 areconnected to leads 46, 48 from the heating element 32. Two temperaturesensors 50, 52, such as thermocouples, thermistors, or any othersuitable temperature sensing devices, are embedded in the foaminsulating jacket 34 adjacent the heater mat 30 so that they can detecttemperatures at or near the heater mat 30. Signals from one of thetemperature sensors, e.g., temperature sensor 52, is used by thecontroller 20 for normal operational or process heater controlfunctionality, and signals from the other temperature sensor, e.g.,temperature sensor 50, is used by the controller 20 for uppertemperature limit control, as will be described in more detail below.One temperature sensor could be used for both of those functions, but itis better to provide the redundancy of two temperature sensors,especially for the high temperature limit function, which has to shutdown the heater if the process temperature sensor and/or the processcontrol circuit in the controller fails and causes a runaway heatersituation. Some safety certifying agencies require such redundancy forsafety certification.

The low voltage wires 54, 56 for the first (“high-limit”) temperaturesensor 50 and 58, 60 for the second (“process”) temperature sensor 52are routed through the cavity 40 and through a flexible cord 62 to acable connector 64, for example, a Molex™ connector. A boot 66 anchorsthe flexible cord 62 to the pipe heater 16 and covers the cavity 40. Theheater cord 62 can be any desired length. In some embodiments, the cord62 is long enough to place the controller 20 (FIGS. 1-8) and connector64 far enough away from the heater 16 to avoid heat damage to thecontroller 20, especially in high temperature applications. Of course,as shown in FIGS. 1-8, the controllers 20 are connected to the pipeheater 16 through the connector 64, either directly as illustrated inFIGS. 1-4 for the individual heater control configuration 14 or via aslave adapter 22 and slave heater cables 24 (FIG. 5) and 184 (FIG. 18),as will be described in more detail below.

Before proceeding further with structural details of individualcomponent parts of the multiple heater control system, reference is madenow to FIG. 27, which, in conjunction with FIGS. 1 and 9, provides anoverview of some of the electrical components and functions of thesystem and is helpful for an understanding of other components andfeatures that will be described below. Therefore, as shown in FIG. 27with secondary reference to FIGS. 1 and 9, a plurality of controllers 20can be connected individually to respective heaters 16 primarily, butnot exclusively, for providing controlled AC power to the heaters 16 inorder to maintain the heaters 16 operating within certain desiredtemperature ranges.

A daisy chain connected series of cable sections 25, 26, 108 thatconnect together in daisy chain fashion to form a source power trunkline that delivers AC source power to the controllers 20. Thecontrollers 20 then switch the AC power on and off to deliver thecontrolled AC power to the heaters 16, as necessary for the heaters 16to produce the heat needed for maintaining the desired temperatures. Thecontrollers 20 turn the AC power on and off with a process power switcharrangement 302, which can be a solid state switch, such as a triac 303,in parallel with a mechanical relay 305 to minimize arcing and heatproduction, or any other controllable switch to produce the controlledAC power. It is also possible to use a variable power controller, suchas a variac transformer (not shown), for adjusting the controlled ACpower up and down, but they are much larger, bulkier, and more expensivethan switch devices. Control of the process power switch arrangement 302using temperature signal feedback from the second (process) temperaturesensor 52 in the heater 16 is described in more detail below.

A high temperature limit switch (also called a high-limit switch) 300 isalso provided for shutting off the AC power to the heater 16 in theevent the temperature of the heater 16 rises to an unsafe level assensed by the first (high-limit) temperature sensor 50. Such an unsafetemperature level could be due to a malfunction of the process powerswitch 302, the process temperature sensor 52, or the process controlcircuit 296 (FIG. 28), or it could be due to some external cause, suchas a high temperature purge or cleaning cycle in the pipe, or any othercause. Control of the high-limit switch 300 using temperature feedbackor input from the temperature sensor 50, including a latching functionto keep the AC power turned off once it has been turned off pending anoperator intervention, is described in more detail below.

An alert/alarm function is also provided, which signals an alert/alarmat the remote monitor station 15 when any one of the controllers 20 inthe daisy chain connected series detects that the heater 16 which itcontrols is at a temperature above or below a desired or neededoperating temperature range. For example, if it is necessary to keep thepipe P (FIG. 9) within a certain temperature range for a chemicalprocess, transport, or other activity to proceed, this alert/alarmfunction 17 can notify an operator at the remote monitor station 15 ifany one of the controllers 20 detects a heater 16 temperature outside ofthat temperature range, and/or it can produce a signal to an equipmentinterlock 19 to prevent operation of, or shut down of, equipment untilthe heaters 16 are all producing temperatures in the desired range, aswill be understood by persons skilled in the art. The depiction of themonitor station 15 in FIG. 27 as a defined block is only schematic. Thevarious components and functions, e.g., DC power supply 21, continuitydetector 31, signal circuit 23, and alert/alarm 17, can be in onelocation or in divers locations, so the use of the term “remote monitorstation” in this description is for convenience only and does not limitthe components or functions described or depicted to being together atone location or in any unitary configuration or assemblage.

To implement this alert/alarm function (also sometimes called thetemperature range signal), a low voltage DC power supply 21 at theremote monitoring station 15 provides a low voltage DC potential on asignal circuit 23 comprising a pair of conductors 27, 29 that runs viathe daisy chain cable sections 25, 26, 108 to all of the controllers 26.Low voltage is generally considered to not exceed 30 volts, which is howthe term is used herein. Therefore high voltage is anything above 30volts. One of the conductors, e.g., conductor 29, extends through eachcontroller 20, where it is connected in series to opposite terminals ofa relay switch 310. Therefore, any of the series connected relayswitches 310 in any of the controllers 20 can open the circuit 23, i.e.,prevent current from flowing in the signal circuit 23. Conversely, allof the relay switches 310 in all of the controllers 20 have to be closedin order for the signal circuit 23 to be closed. The term “relay switch”as used herein can mean any switch, mechanical or solid state, in whicha control signal input can be applied to open and/or close the switch,i.e., to block and/or allow current flow through the switch.

A continuity detector 31 associated with the remote monitoring station15 detects whether the signal circuit 23 is opened or closed. Upondetection that the signal circuit is open, which can be caused by any ofthe relay switches 310 being opened or by any disconnect or break in thedaisy chain cables 25, 26, 108, the continuity detector 31 generates asignal to the alert/alarm 17 and/or to an equipment interlock 19, or toany other device or function desired by the operator. In other words,the signal from the continuity detector 31 can be used to initiate analert or alarm, or it can be used to stop equipment in any use, as willbe apparent to persons skilled in the art upon reading this description.A variety of continuity detectors that can perform this function, e.g.,current detector circuits, voltage detector circuits, and the like, arereadily available and well known to persons skilled in the art or caneasily be constructed by persons skilled in the art, so no furtherdescription is required for an understanding of this feature. Forconvenience, but not for limitation, the signal circuit 23 is sometimescalled the “alert/alarm signal circuit” or “temperature range signalcircuit”, even though the signal can also be used for equipmentinterlock and other purposes.

The relay switch 310 in each controller 20 is controlled to open andclose by a process control circuit (FIG. 28) in the controller 20, whichuses temperature information from the process temperature sensor 52 todetermine if the sensed temperature at the heater 16 connected to thatcontroller 20 is within the desired operating range. If not, it outputsa signal to open the relay switch 310, which opens the signal circuit23. The open signal circuit 23 is detected by the continuity detector31, which generates the alert/alarm signal. The relay switch 310 can bea mechanical relay or a solid state relay, as is well known to personsskilled in the art.

The daisy chain connection components for connecting the controllers 20electrically to the AC power source 13 and to the temperaturealert/alarm circuit 23 at the remote monitoring station includes atleast one T-type source power/signal cable section 26 (“T-type sourcepower/signal cable” or “T-type source power cable” or just “T-typesource cable” for short) and at least one linear-type terminating linearsource power/signal cable section 108 (“linear-type power/signalterminating cable” or “linear-type terminating source power cable” orjust “terminating source cable” for short) as shown in FIGS. 1-4 and 27.The T-type source cables 26 are used to connect the first andintermediate controllers 20 in the daisy chain connected series to theAC power source 13 and to the alert/alarm signal circuit 23. Theterminating source cable 108 is used to connect the last controller 20in the daisy chain connected series to the AC power source 13 and to thealert/alarm signal circuit 23 via the T-type source cable(s) 26, asshown in FIGS. 1-4 and 27. The first T-type source cable 26 can beconnected directly to the monitor station 156 if it is close enough, or,as shown in FIG. 27, an optional linear-type source power/signalextension cable (“source power/signal extension cable” or just “sourceextension cable” for short) 25 of any necessary length, can be used toconnect the first T-type source cable 26 to the monitor station 15, asindicated schematically in FIG. 27.

To implement the functions of providing AC source power to the series ofdaisy chain connected controllers 20 and routing the alert/alarm signalcircuit 23 through the relay switches 310 in each of the controllers 20,as described above, the T-type source cables and the linear-type sourcecable 108 (and optional source extension cable 25, if needed) areconstructed and configured not only to perform those electricalfunctions, but also to provide a neat, tidy appearance. The structureand configuration also makes it almost foolproof to connect the AC powersource and alert/alarm signal circuit 23 with as many controllers 20 asdesired. As shown in FIG. 27, each terminating source cable 108 isfairly straight forward in that one pair of high voltage wires 114, 116(“AC power wires” or just “power wires” for short) and one pair of lowvoltage wires 118, 120 (“signal wires” for short) extend all the waystraight through the terminating source cable 108 from the inletconnector 110 to the outlet connector 112.

Any type of connector that can connect four wires from one cable to fourwires of another cable can be used. Molex™ connectors work well becausethey are available in configurations that accommodate four, six, or morehigh voltage and low voltage wire pairs in a manner that mates withcorresponding connectors on other components in only one orientation sothat they cannot be improperly connected. Also, both the male and femalepins are sheathed so it is difficult to accidentally short them. In thisdescription, for convenience and not for limitation, the term “inlet” isused to designate the connector or cable end that receives AC sourcepower and the term “outlet” is used to designate the connector or cableend that delivers AC source power, regardless of whether thoseconnectors or cable ends also receive and/or deliver low voltagesignals.

For the linear-type terminating source cable 108, the inlet connector110 has at least two power pins for the AC source power wires 114, 116and at least two signal circuit pins for the signal circuit wires 118,120 and is configured to mate with a trunk outlet connector 86 on theT-type source cable 26. The outlet connector 35 at the remote monitoringstation 15, which delivers source power to the daisy chain components25, 26, 108 and connects the signal circuit 23 to those components, isalso configured the same as the trunk outlet connector 86 on the T-typesource cable 26. Therefore, the inlet connector 110 of the terminatingsource cable 108 could be plugged directly into the monitoring stationoutlet connector 35 in situations where there is only one controller 20in a heater system.

As will be discussed in more detail below, the terminating source cable108 has to be used to connect the last controller 20 in a daisy chainconnected series or the only controller 20, if there is only one, to theremote monitoring station 15 so that the signal circuit 23 can beclosed. A daisy chain terminated with a T-type source cable 26 wouldleave the signal circuit 23 open, regardless of whether all of the relayswitches 310 in all of the controllers 20 are closed, which would rendersignal circuit 23 inoperative for its intended purpose as describedabove.

The outlet connector 112 of the terminating source cable 108 also needsat least two power pins for the source power wires 114, 116 and at leasttwo pins for the signal circuit wires 118, 120, and it is configured tomate with the inlet connector 140 of the controller 20. The inletconnector 140 of the controller 20 has a different configuration thanthe inlet connectors 82, 110 of the T-type source cables 26 andterminating source connectors 108, respectively, so the outlet connector112 of the terminating source cable 108 also has to be different thanthe trunk outlet connectors 86 of the T-type source cables and differentthan the outlet connector 35 at the remote monitoring station 15. Thisdifferent configuration for the inlet connectors 140 of the controllers20 is provided for the purpose of orderly use of one AC source powercable section per controller, which is easy for users. Of course, theinlet connector 140 of the controller 20 could have the sameconfiguration as the inlet connectors 82, 110, if desired.

The T-type source cables 26 are used for connecting the first and anyintermediate controllers 20 to the source power circuit 33 and thesignal circuit 23 at the remote monitoring station 15, as mentionedabove. Each T-type source cable 26 has a trunk section 83 extendingbetween the inlet connector 82 and the trunk outlet connector 86 and abranch section 85 extending from the trunk section 83 to the branchoutlet connector 78. As best seen in FIG. 29, the trunk power wires,comprised of power wires 86, 88 of the inlet trunk segment 70 and thepower wires 90, 92 of the outlet trunk segment 72 extend uninterruptedbetween the trunk inlet connector 82 and the trunk outlet connector 86.The branch power wires 89, 91 are connected electrically in parallel tothe trunk power wires 87, 88 and to the branch connector 78 so that,when the controller 20 is connected to the branch section 85, the powercircuit comprising the power conductors 290, 292 in the controller 20are in parallel electrically with the trunk power wires 87, 88 and withthe power circuits comprising the power conductors 290, 292 in the otherdaisy chain connected controllers 20. In the T-type source cable 26shown in FIGS. 10, 11, the branch wires are very short jumpers withinthe connector 78 itself, and, alternatively, they could even beeliminated by joining wires 87, 88 and 90, 92 together at or adjacentthe pins 2, 1, all of which are equivalents as will be understood bypersons skilled in the art.

The signal wires 98, 102 in the inlet trunk segment 70 and outlet trunksegment 72 are connected together to extend electrically uninterruptedthrough the trunk 83 of T-type source cable 26 from the inlet connector82 to the outlet connector 86, electrically bypassing the branch segment85 and the branch outlet connector 78. The other signal wires 100, 104,of the signal wire pairs in the T-type source cable 26, however, detourfrom the trunk section 83 to extend through the branch section 85 torespective separate pins in the branch outlet connector 78. Therefore,when the branch outlet connector 78 is connected to the controller 20,the signal circuit 23 extends in series through the relay switch 310 inthe controller 20. With multiple controllers 20 daisy chain connected inthis manner, all of the relay switches 310 of all the controllers 20 areconnected in series in and to the extended signal circuit 23, so all ofthe relay switches 310 in all of the controllers 20 have to be closed inorder to have a closed signal circuit 23, as explained above. The branchoutlet connector 72 is configured to mate with the inlet connector 140of the controller 20 and the trunk outlet 86 is configured to mate withthe inlet connector 82, so that any number of the T-type source cables26 can be daisy chain connected together to deliver source power to anynumber of controllers 20, while maintaining continuity in the signalcircuit 23, as explained above.

As also mentioned above, the extension source cable 25 shown in FIG. 27can be provided in any length needed to connect the daisy chaincomponents 26, 108 to the source power 33 and the signal circuit 23 atremote monitoring station 15. The power wire pair 93, 95 and the signalwire pair 97, 99 extend electrically uninterrupted from the inletconnector 101, which is configured to mate with the outlet connector 35at the remote monitoring station 15, to the outlet connector 103, whichis configured to mate with the inlet connector 82 of the T-type sourcecable 26 and with the inlet connector 110 of the terminating sourcecable 108.

Referring now primarily to FIG. 10 in conjunction with FIGS. 1-9, theT-type source cable 26 can, but does not have to, comprise two coiledtrunk cable segments 70, 72 fastened together with a band 74 to form aneat, T-shaped, coiled, source power cable section 26. Both of the trunkcable segments 70, 72 have respective ends 74, 76 that are terminated inthe common branch cable connector 78. The other end 80 of the inlettrunk cable segment 70 is terminated in the inlet cable connector 82,and the other end 84 of the outlet trunk cable segment 72 is terminatedin the outlet trunk connector 86. Any suitable cable connectors can beused, for example, Molex™ connectors, as discussed above.

FIG. 11 is a schematic circuit diagram of the T-type source cable 26.Each trunk segment 70, 72 contains at least two power wires, e.g., thepower wires 86, 88 in trunk segment 70 and the power wires 90, 92 in thetrunk segment 72, for carrying source power to the controllers 20. Thepower wires 86, 88 in the inlet trunk cable segment 70 are terminated inpins 1, 4 in trunk inlet connector 82 and in pins 1, 2 in the commonbranch outlet connector 78. The power wires 90, 92 in the outlet trunkcable segment 72 are terminated in pins 1, 4 in trunk outlet connector86 and in pins 5, 6 in the common branch outlet connector 78. Sourcepower from a source, for example, the AC power supply 13 (FIG. 27), isusually connected to the inlet trunk segment 70 via the trunk inletconnector 82, and both trunk segments 70, 72 are connected to acontroller 20 via the common branch outlet connector 78 (see FIGS. 1-8),so source power is supplied to the controllers 20 via pins 1, 2 in thecommon connector 78. However, by-pass connections 94, 96 are provided toconnect the power wires 86, 88 to the power wires 90, 92 in the outlettrunk cable segment 72 in order to supply source power to the pins 1, 4in the trunk outlet connector 86 for other controllers 20 and pipeheaters 16 that may be daisy chain connected to the trunk outletconnector 86 as described above.

One of the low voltage signal wires, e.g., wire 98, in the inlet trunksegment 70 is connected directly to a corresponding signal wire 102 inthe outlet trunk segment 72 so that pin 3 in connector 82 of the inlettrunk segment 70 is at a common potential with pin 3 in the trunk outletconnector 86 of the outlet trunk segment 72. However, those signal wires98, 102 by-pass the branch outlet connector 78, so they do not getconnected to the controllers 20. The other signal wire 100 in inlettrunk segment 70, however, does connect the pin 6 in the trunk inletconnector 82 to a pin 4 in the branch connector 78. Likewise, the othersignal wire 104 in the outlet trunk segment 72 connects pin 6 in thetrunk outlet connector 86 to pin 8 in the common branch outlet connector78. Therefore, the controllers 20 can either close or open the signalcircuit comprising the two signal wires to either maintain or interrupta closed circuit comprising the signal wires, for example, to cause thecircuit continuity detector to detect that the signal circuit 23 isopened and to trigger the alert/alarm at the remote monitoring station15 (FIG. 27) in the event the controller 20 detects a heater problem orto trigger some other function, as mentioned above. The unused pins 2, 5in the trunk inlet connector 82, the unused pins 3, 7 in the commonbranch outlet connector 78, and the unused pins 2, 5 in the trunk outletconnector 86 are optional and can serve the function of maintaining aspatial distance between high and low voltage connections to avoidelectrical noise or interference in the low voltage signals by the highvoltage AC power.

The linear-type terminated source power cable 106 shown in FIG. 12 isused to connect AC source power and the signal circuit 23 to the lastcontroller 20 in a daisy chained plurality of controllers 20 oroptionally to a sole controller 20 in a heater system that has only onecontroller 20, as mentioned above. It comprises one cable 108,preferably, but not necessarily, coiled to maintain a neat structure. Itis terminated at one end with the inlet connector 110 that mates withthe trunk outlet connector 86 of the T-type source cable 26 and at theother end with the outlet connector 112 that, like the branch outletconnector 78 of the control power cable 26, mates with the inletconnector 140 (FIGS. 20-21 and 29) on the controllers 20. As shown inthe schematic circuit diagram in FIG. 13, this terminated source cable106, like the T-type source cable 26, contains at least two power wires114, 116 and at least two signal wires 118, 120. The power wires connectthe pins 1, 4 of the inlet connector 110 to pins 2, 1 of the outletconnector 112, and the signal wires connect pins 3, 6 of the inletconnector 110 to the pins 8, 4 of the outlet connector 112. Theterminated source cables 106 are used to provide source power from an ACpower source 13 (FIG. 27) and the signal circuit 23 from the remotemonitor station 15 (FIG. 27) to the last controller 20 in a series ofdaisy chain connected controllers 20, instead of using a T-type sourcecable 26, because the T-type source cables 26 at the end of a daisychain would leave the two signal wires unconnected, thus always an opencircuit voltage situation that would prevent operation of thetemperature range alert/alarm signal function, which will be describedin more detail below.

In the single point control configuration 14 for zoned master and slaveheaters shown in FIGS. 5-8, a single controller 20 is connected via aslave adapter, for example, the slave adapter cable 22 or a slaveadapter junction box 324 described below in relation to FIGS. 33-36, toone or more T-type controlled slave cables 24 to control a plurality ofheaters 16, 16′ in a ganged group or zone of heaters with the singlecontroller 20. The first heater 16 in the zone, which is connected tothe single controller 20 by the slave adapter cable 22, is considered tobe the master heater for the zone because the controller 20 responds totemperature sensors 50, 52 (FIG. 9) in that first heater 16 to controlboth that master heater 16 and the rest of the slave heaters 16′ in thezone. The rest of the heaters 16′ in the zone, other than the masterheater 16, are called the slave heaters, because they simply heat or notheat as the AC power is switched on and off, i.e., controlled, by thecontroller 20 without providing any temperature feedback to thecontroller 20. For convenience, the T-type controlled power slave cables24 are so designated because they carry controlled AC power from thecontroller 20 to the slave heaters 16′, as opposed to the T-type sourcepower cables 26 described above, which carry AC source power to thecontrollers 20.

The master heater 16 and the slave heaters 16′ in typical installationsare usually identical for convenience and standardization, which is howthey are shown and described herein as an example, although identicalmaster and slave heaters is not a requirement for every embodiment ofthe invention. The slave heaters are designated 16′ instead of 16 justfor convenience in this description for indicating their slavedfunctions as distinct from the master functions of the master heater 16.As will be explained in more detail below, the temperature sensors 50,52 (FIG. 9) in the slave heaters 16′, if they exist, are not used.Therefore, the slave heaters 16′ could be made without temperaturesensors, if desired, and still be used with this invention. However, asmentioned above, the slave heaters 16′ can be the same as the masterheater 16, in which case the slaved heater cables 22, 24, 184 used forconnecting the slave heaters 16′ to the controller 20 are configured ina way that isolates the temperature sensors 50, 52 (FIG. 9) in the slaveheaters 16′ and that does not route the signals from those temperaturesensors to the controller 20, thereby rendering the temperature sensors50, 52 of the slave heaters 16′ effectively inoperative in the system,as will be described in more detail below.

As indicated in FIGS. 5 and 8, there can be any number of slave heaters16′ in the grouping or zone controlled by the one controller 20.Subsequent slave heaters 16′ in the zone can simply be connected in adaisy chain manner to the last T-type controlled slave cable 24 shown inFIGS. 1 and 4 by additional T-type controlled slave cables 24 and aterminating controlled cable 184 (FIG. 18), which is not shown in FIGS.5-8 but will be described in more detail below.

To summarize, the T-type controlled slave cables 24 only conductelectricity to the heater coils (FIGS. 9 and 32) in the slave heaters16′. The electricity for powering the slave heaters 16′ is controlled bythe controller 20, so when the controller 20 switches on electric powerto the slave heaters 16′, they produce heat. When the controller 20switches off the electric power to the slave heaters 16′, they stopproducing heat. No temperature information is derived by the controller20 from any of the slave heaters 16′.

The master heater 16 also produces heat when the controller 20 switcheson the electric power, and it stops producing heat when the controller20 switches off the electric power. However, the controller 20 alsoreceives temperature information from temperature sensors 50, 52 (FIGS.9 and 32) in the master heater 16 and turns the power on and off inresponse to sensed temperature levels in the master heater 16.Therefore, when the sensed temperature in the master heater 16 is low,based on settings in the controller 20, the controller 20 will turn onthe power, and all of the master and slave heaters 16, 16′ in the zonewill be turned on in unison. Likewise, when the temperature sensed inthe master heater 16 is high, based on settings in the controller 20,the controller 20 will turn off the power, and all of the master andslave heaters 16, 16′ in the zone will be turned off in unison.

Electric power is provided to the controller 20 in FIG. 5 via a T-typesource power cable 26. The T-type source cable 26 looks similar to theT-type controlled power slave cables 24 from the outside, but it alsohas at least a pair of low voltage signal wires in addition to the pairof high voltage power wires, as described above, whereas the T-typecontrolled power slave cables 24 have the pair of high voltage powerwires for powering the heater elements in the slave heaters 16′ but notthe signal circuit wires for the alert/alarm circuit described above.

The slave adapter cable 22 shown in FIG. 14 is used, as shown in FIGS.5-8, to connect a controller 20 to the master heater 16 and to one ormore slave heaters 16′, as explained above. The slave adapter cable 22is comprised of two cable segments, a master controlled power cablesegment 126 and a slave controlled power cable segment 128, which are sodesignated for convenience because they carry controlled (e.g., switchedon and off) power from the controller 20 as opposed to source power tothe controller 20. One end 127 of the master controlled power cablesegment 126 is terminated at an inlet connector 130, which, like theinlet connector 64 on the heater cord 62 (FIGS. 1-9), has at least sixpins to handle at least two high voltage power wires to conduct ACcontrolled power to the heating element 32, and two pairs of signalwires for the two temperature sensors 50, 52 (FIG. 9) in the masterheater 16 (FIGS. 5-9). In some embodiments, the signal wires can be lowvoltage, while in other embodiments at least one of the pairs of signalwires may also be high voltage, depending on the kind of temperaturesensor used for the high-limit control, as will be described in moredetail below. Therefore, the inlet connector 130 can be the sameconfiguration as the inlet connector 64, which provides the option ofconnecting a heater cord 62 directly to the output connector 142 in thecontroller 20, as is shown in FIGS. 1-4 for the individual local heatercontrol configuration 12, or of connecting the heater cord 62 to acontroller 20 via a slave adapter 22, as is shown in FIGS. 5-8 for thesingle point control configuration 14 for a zone comprising master andslave heaters. The other end 129 of the master controlled power cablesegment 126 is terminated at a common outlet connector 132, which isconfigured like the outlet connector 142 on the controller 20 (FIGS. 3,7, 20, 21) so that it can mate with the inlet connector 64 of the heatercord 62, which, again, provides the option of connecting the heater 16directly to a controller 20 for individual heater 16 control or to theslave adapter 22 for a single point control configuration 12. The slavecable segment 128 of the slave adapter 22 contains two high voltagepower wires for powering the slave heaters 16′, but it does not have tohave wires for the temperature sensors 50, 52, as will be explained inmore detail below. One end 136 of the slave cable segment 128 isterminated in the common outlet connector 132 and the other end 138 isterminated in a slave outlet connector 134.

As shown in the schematic circuit diagram in FIG. 15 for the slaveadapter cable 22, and as mentioned above, the master cable segment 126has at least two power wires 144, 146, which connect pins 1, 5 of theinlet connector 130 to pins 1, 5 of the outlet connector 132 forproviding high voltage AC power to the heater elements 32 in the masterheater 16 (FIGS. 1-4 and 9). The master cable segment 126 also has twopairs of signal wires, e.g., a first pair of wires 148, 150 and a secondpair of wires 152, 154, for connecting the two temperature sensors 50,52 (FIG. 9), respectively, in the master heater 16 to the single pointcontroller 20 (FIGS. 5-8). The signal wire pair 148, 150 connect pins 4,8 of inlet connector 130 to pins 4, 8 of the outlet connector 132, andthe other signal wire pair 152, 154 connect pins 3, 7 in the inletconnector 130 to pins 3, 7 in the outlet connector 132. However, asexplained above, the controller 20 in the single point controlconfiguration 14 (FIGS. 5-8) gets temperature information only from themaster heater 16, not from the slave heaters 16′. Therefore, the slavecable segment 128 of the slave cable adapter 22 does not need any signalwires. Its only function is to provide controlled high voltage power tothe slave heaters 16′, so the slave cable segment 128 contains two highvoltage power wires 156, 158, as shown in FIG. 11. Also, by not havingsignal wires in the slave cable segment 128, use of the slave cableadapter 22 automatically isolates the temperature sensors 50, 52 ofsubsequent heaters in a daisy chain, which makes them function as slaveheaters 16′. Also, since there does not have to be any signal wires inthe slave cable segment 128, the outlet connector 134 can be simplerwith fewer pins than the connectors 130, 132. Also, this smaller outletconnector 134 with its different configuration prevents mistakenconnection of a source power cable 26 or a terminated source power cable106 to the slave adapter cable 22, which could inadvertently connect thetemperature sensors 50, 52 of more than one heater 16 to the singlepoint controller 20. Of course, the smaller, differently configuredconnector 134 also requires a smaller mating connector 172, 190 onsubsequent slave heater cables 24, 184, which will be discussed in moredetail below. Those smaller connectors 172, 190 also prevent those slavecable sections 24, 184, which do not have signal wires, from beinginadvertently connected into the power/signal trunk line, which doeshave signal wires, as described above.

As shown in FIG. 15, the high voltage power wires 156, 158 of the slaveadapter cable 22 connect pins 1, 5 of the connectors 130, 132 to thepins 1, 3 of the outlet connector 134 so that high voltage source powerprovided from the controller 20 (FIGS. 5-8) through the inlet connector130 is also provided to the outlet connector 132 for the master heater16 and to the outlet connector 134 for the slave heaters 16′. Again, thepins 2, 6 in the connectors 130, 132 are unused and provide spacebetween the high voltage connections and the signal connections. Pins 2,4 in the outlet connector 134 are not used.

The T-type controlled power slave cable 24 is best seen in FIG. 16, andits schematic circuit diagram is shown in FIG. 17. This T-typecontrolled power cable 24 comprises two trunk segments 160, 162,preferably, but not necessarily, coiled and banded together with a band164 to create and maintain a neat structure. Since this T-typecontrolled power cable 24 only provides high voltage controlled power tothe slave heaters 16′ (FIGS. 5-8) as discussed above, these first andsecond slaved trunk segments 160, 162 contain high voltage power wires166, 168, but they do not have to contain any signal wires. Further,with no signal wires in the T-type controlled power slave cable 24, theselection and use of these T-type controlled power slave cables 24 toget controlled AC power to a heater, instead of connecting a controller20 directly to the heater, automatically isolates the temperaturesensors 50, 52 of the heater, thus makes the heater function as a slaveheater 16′ instead of as master heater 16. Also, since the branch outletconnector 78 of the T-type source power cable 26 described above isconfigured different from the branch outlet connector 170 of the T-typecontrolled power slave cable 24 in the example embodiment describedabove, the T-type source power cable 26, which does have signal wires,cannot be connected to the heater.

One end of each trunk segment 160, 162 of the T-type controlled powerslave cable 24 is terminated in a common branch outlet connector 170,and the opposite end of the inlet trunk segment 160 is terminated in ainlet daisy chain connector 172 while the opposite end of the slaveoutlet trunk segment 162 is terminated in a trunk outlet slave daisychain connector 174. The slave inlet daisy chain connector 172 isconfigured to mate with the slave outlet daisy chain connector 134 ofthe slave adapter cable 22 (FIGS. 5-8 and 14). The trunk outlet slavedaisy chain connector 174 is configured the same as the daisy chainoutlet connector 134 of the slave adapter cable 22 so that any T-typecontrolled power cable 24 can be connected either to the slave adaptercable 22 or to another T-type controlled power cable 24.

The common slaved heater outlet connector 170 is configured to mate withthe inlet connector 64 of the heater cord 62 so that it can deliver highvoltage power to the slave heaters 16′ (FIGS. 5-8). Therefore, eventhough the T-type controlled power cable section 24 does not have tohave any signal wires, the common slave branch outlet connector 170 isthe same configuration as the outlet connector 132 of the slave adaptercable 22 and as the outlet connector 142 in the controller 20 so that itcan mate with the inlet connector 64 of the heater 16′. As shown in FIG.17, the high voltage controlled power wires 176, 178 in the slave inlettrunk segment 160 connects the pins 1, 3 of inlet connector 172 to thepins 1, 5 of the common branch outlet connector 170, which is the sameas the high voltage power connections to pins 1, 5 in the outletconnector 132 of the slave adapter cable 22. The high voltage powerwires 176, 178 of the inlet trunk segment 160 are also connected to thehigh voltage power wires 180, 182 of the outlet trunk segment 162 inorder to provide high voltage power at the pins 1, 3 of the outlet slavedaisy chain connector 174. As shown in FIG. 17, there are numerousunused pins 2-4 and 6-8 in the branch outlet connector 170, but havingno signal wires connected to the pins 3, 7 and 4, 8 isolates thetemperature sensors 50, 52 in the pipe heater 16′ and prevents them frombeing connected to the controller 20, which makes the heater function asa slave heater 16′.

It should be apparent from this description, therefore, that the sameheaters can be used as either: (i) individually controlled heaters 16 inan individual local heater control configuration; (ii) a master heater16 in a single point heater control configuration; or (iii) a slaveheater 16′ in a single point control configuration. No modification orchange is needed in either the controller 20 or the heater 16 to makethis selection or to implement these functions. The desired function ofthe heater—individually controlled, master, or slave—is implementedmerely by choosing to either: (i) connect the heater directly to acontroller 20 for an individually controlled heater 16; (ii) connect theheater to controller 20 via a slave adapter, e.g., a slave adapter cable22, for a master heater 16; or (iii) connect the heater to a controller20 via a slaved heater controlled power cable section 24 for a slaveheater 16′.

The selection of a heater to function as a slave heater 16′ can also bemade for the last slave heater 16′ in a zone of heaters in a singlepoint heater control configuration by using a terminated controlledpower cable 184, which is best seen in FIG. 18 with its schematiccircuit diagram in FIG. 19. Essentially, the terminated controlled powercable 184 is substantially the same as the inlet trunk segment 160 ofthe T-type controlled power cable 24 (FIG. 16). It only has to have twohigh voltage power wires 186, 188, a inlet connector 190 that is thesame as the inlet connector 172 in the T-type controlled power cable 24,and an outlet connector 192 that is the same configuration as the outletconnector 170 of the T-type controlled power cable 24. The high voltagepower wires 186, 188 connect the pins 1, 3 in the inlet connector 190 tothe pins 1, 5 in the outlet connector 192. In use, the outlet connector192 is connected to the inlet connector 64 on the heater (FIG. 9), whichmakes it a slave heater 16′ because there are no signal wires connectedto the pins 3, 7 and 4, 8 of outltet connector 192, which isolates thetemperature sensors 50, 52 in the heater (FIG. 9), as explained above.The inlet connector 190 can be connected to the outlet connector 134 ofthe slave adapter cable 22 (FIGS. 5-8 and 14), if there is only oneslave heater 16′, or to a connector 174 of the T-type controlled powercable 24, if the heater 16′ is the last in a series of more than oneslave heater 16′.

The controller 20 is modular so that it can be used in a simplerarrangement with factory-preset parameters or so that it can beexpanded, if desired, to accommodate more user interface and settableparameter options. As best seen in FIGS. 20-23, the controller 20 has abase module 200, which includes circuit components that are necessaryfor the basic functions of the controller 20 with factory-presetparameters, including, but not limited to: (i) Monitoring thetemperature sensors 50, 52 in the heater 16 (FIG. 9); (ii) Turning thehigh voltage power to the heater elements 32 on and off according tofactory-preset temperature parameters and hysteresis; (iii)Disconnecting the high voltage power in the event of an over-temperatureevent according to a factory-preset upper temperature limit; (iv)Initiating an alarm signal to a remote monitoring station if the highvoltage power is disconnected due to a high-temperature event; and (v)Displaying several status indicators, e.g., low temperature, hightemperature, in-range, high voltage power to the heater(s) on or off,and high voltage power disconnected due to a high temperature event.

Additional functionality and user interface capabilities, such asre-settable parameters, data communications, system monitoring,alpha-numeric visual display capabilities, and others can be added tothe controller 20 by attaching an expansion module 202 to the basemodule 200, as shown by FIGS. 21 and 22, as well as in FIGS. 2, 3, 6,and 7. The example expansion module 202 shown in FIGS. 21 and 22includes a circuit (not shown in FIGS. 21 and 22) that processes userinputs either from inputs on the expansion module 202 itself or from aremote location via the communication components or other communicationsimplementations as explained below. It also communicates with processcontrol and, in some embodiments, with high temperature limit controlcircuits 296, 298 (FIG. 29) in the base module 200 to view, set, reset,and monitor some or all functions of the base module 200 depending onthe level of adjustability built into the base module 200 and the levelof capabilities built into a particular expansion module 202. As shownin FIG. 21, the expansion module 202 has an alpha-numeric display 204that is visible through a transparent front face portion 206 of ahousing 208, user input buttons 210, 212, 214, and status LED displaynubbins 216, 218, 220, all of which will be discussed in more detailbelow. The expansion module 202 can also have data line communicationports 222, 244 to transmit and receive data to and from a remote stationand/or to and from another controller 20 in a daisy chain connectedsystem. It should also be noted that different expansion modules 200 canalso be made with fewer than or more than these features so that userscan select and install particular expansion modules with a particularpackage of capabilities and features, depending on what they want orneed for their particular heater control systems. Also, wirelesscommunication components, such as infrared, RF, or other wirelesscommunications implementations and components for such implementations(not shown) can also be included in the expansion module, if desired, asis understood by persons skilled in the art. Therefore, thecommunications ports and components shown in the drawings areexamples—not exclusive or limiting embodiments.

The expansion module 202 attaches very easily to the base module 200 asbest seen in FIGS. 21 and 22 by simply aligning a plurality, e.g.,three, latch dogs 222, 224, 226 protruding from the back side 234 of theexpansion module 202 with a plurality, e.g., three, corresponding ormating latch holes 228, 230, 232 in the front panel 288 of the basemodule 200 and snap it into place. It can be removed just about aseasily by simply pulling the expansion module 202 apart from the basemodule 200.

The circuit board in the base module 20 has a set of electric contacts,for example, the pad of contacts 236, or any other suitable plugreceptacle, and a plurality, e.g., three, LEDs 240, 242, 244 adjacent anopening 246 in the front panel 238. A correspondingly aligned and matingcontact assembly 248, or a suitable plug, protrudes from a circuit boardin the expansion module 202 through the rear panel 256, which, when theexpansion module 202 is snapped into place on the base module 200,protrudes through the opening 246 and into contact with matingelectrical contacts on the contact pad 236 or into the plug receptacle(not shown) in the base module 200 in order to connect the expansionmodule 202 electrically to the base module 200 to receive power and tocommunicate data. Also, there are a plurality, e.g., three, transparentor at least translucent bosses or wave guides 250, 252, 254 mounted inthe circuit board in the expansion module 202 that are aligned with andextend from the display nubbins 216, 218, 220 on the front face 206 toprotrude out the back panel 256 toward the base module 200. Theseprotruding bosses 250, 252, 254 align with the LEDs 240, 242, 244 in thebase module 200, so that, when the expansion module 202 is snapped intoplace on the base module, the bosses 250, 252, 254 are positionedadjacent the LEDs 240, 242, 244 so that they transmit light from theLEDs 240, 242, 244 to the display nubbins 216, 218, 220 on the frontface 206.

When the base model 200 is operated alone, without the expansion module202, a dust cover 258 is provided to snap into place on the base module202 in place of the expansion module 200, as best seen in FIG. 23, inorder to prevent dust and debris from entering the base module 200through the opening 246. The dust cover also has latch dogs similar tothose on the expansion module 202 that align with and snap into thelatch holes 228, 230, 232 to hold the dust cover 258 in place on thebase module 200. The dust cover 258 has three bosses 260, 262, 264similar to the bosses 250, 252, 254, but shorter, that extend from thefront of the dust cover 258 into the hole 246 to the LEDs 240, 242, 244so that they transmit light from the LEDs to the front of the dust coverfor status displays.

Of course, more or fewer LED status displays can be provided for eitherthe expansion model display or the dust cover display. The three LEDstatus displays 216, 218, 220 on the expansion module 202 and the threeLED status display 260, 262, 264 on the dust cover 258 in the exampleembodiment described herein may be, for example, an “Alert/Alarm” whenthe controller 20 detects a condition that needs attention, such as aheater not working so that the sensed temperature, e.g., from theprocess temperature sensor 52, is too hot or too cold, an “In Range”mode to indicate the temperature of the heater is in the preset desiredoperating range, and an “Output” mode, which shows that the controlledAC power to the heater is turned on, i.e., being output to the heater.

As mentioned above, the expansion module 202 can be equipped orprogrammed to provide more or fewer of the functions, capabilities,and/or features described herein. Also, some expansion modules 202 canbe made with more or fewer of these functions, capabilities, and/orfeatures than other expansion modules 202. Also, one of the expansionmodules 202 can be moved from one base unit 200 to another base module200 to check and/or reset parameters in the first controller and then tocheck and/or reset parameters in the second and/or any number ofadditional base modules 200. Therefore, if desired, a single expansionmodule 202 can be used on one or more base modules 200, if desired.

To help hold the controller 20 and associated wiring away from hotheaters, which could damage its electronic components, and to helpmaintain a neat, daisy chained connection layout, the controller 20 isprovided with a convenient wall mount bracket 270 and mating lockingsocket 272 in the back panel 274, as best seen in FIGS. 24-26. Thebracket 270 has a plurality of radially extending ears 276, which aresized to slip through mating radially extending slots 278 betweenadjacent sector plates 280 in the socket 272. Then, when the controller20 is rotated, the ears 276 are captured under the sector plate guides280 so that the bracket 270 cannot be withdrawn from the socket 272.Several backing plate guides 282 on the bracket that are recessedaxially behind the ears 276 contact the sector plate guides 280 when thebracket 270 is inserted into the socket 272, so when the controller 20is rotated about an axis 284 of the socket 272, the sector plate guides280 get captured between the ears 276 and the backing plate guides 282to hold the bracket 270 firmly and securely in the socket 272.

In use, the wall bracket 270 can be fastened to a wall or otherstructure (not shown) by screws or other fasteners (not shown) throughthe holes 286 in the cross piece 288. Alternatively, the bracket 270 canbe fastened to an object, e.g., to a heater 16, with a strap, wire,tape, or other material (not shown) wrapped around the cross piece 288and around the object. The controller 20 is then positioned adjacent thebracket 270, axially aligned with the bracket 270 on axis 284, andaxially pushed toward the bracket 270 to pass the ears 276 through slots278 into the socket 272. The controller 20 is then rotated about theaxis 284 to lock the controller 20 in place on the bracket 270, as shownin FIG. 24. The controller 20 can be easily removed from the bracket 270by reversing those steps.

The functions and control logic in one embodiment can be described byreference primarily to the schematic circuit diagrams in FIGS. 28-31 inconjunction with the logic flow diagram in FIG. 32. The schematiccircuit diagram in FIG. 28 depicts the multiple heater control system 10of the present invention in a single point heater control configuration14 as illustrated in FIGS. 5-8 and described above. In summary, themaster heater 16 is connected to the controller 20 via a slave adaptercable 22 to the base module 200 of controller 20. The controller 20 isconnected to a high voltage power source, e.g., an AC power supply, bythe T-type source power cable 26 connected to the controller 20. Thehigh voltage source power is delivered to the controller 20 by the highvoltage wires 86, 88 in the T-type source power cable 26 and isrepresented in the controller 20 by high voltage conductors 290, 292. Inthe controller 20, the high voltage source power is tapped by a DC powersupply 294 which supplies low voltage DC power to the process controlchip 296, to a high limit control chip 298 in the embodiment shown inFIGS. 28-31, and to the contact pad 236 or plug receptacle (not shown),where it is available to the expansion module 202, if the expansionmodule 202 is installed. The high voltage controlled power is alsorouted to the outlet connector 142, where it is available to heaters 16,16′ via the slave adapter cable 22, T-type slave controlled power cable24, and slave terminating controlled power cable 184. In the masterheater 16 and slave heaters 16′, the high voltage controlled power fromconductors 290, 292 in the controller is conducted to the heaterelements 32 by the high voltage wires 42, 44.

In the example controller 20 embodiment shown in the schematic diagramsin FIGS. 28-31, the high-limit control circuit 298 is depicted asincluding a digital logic circuit, such as a microprocessor, which canbe programmed to perform the high-limit cutoff functions. In such adigital logic, high-limit control circuit, one high voltage conductor292 is routed directly to the outlet connector 142, from where itconnects directly to the high voltage wire 44 in each heater 16, 16′.However, the other high voltage conductor 290 is routed through twoswitch devices 300, 302. The first switch device 300 is in front of thesecond switch device 302 and is controlled by a microprocessor or otherlogic circuit in high-limit control circuit 298 to disrupt and turn offthe high voltage power to everything behind the first switch device 300,including all the heaters 16, 16′ and the second switch device 302.Therefore, when the high limit control 298 opens the first switch 300,such as due to an excess temperature event, nothing downstream from therelay switch can operate until the first switch 300 is reset. In thisdescription, “upstream” and “in front of” refers to the side, direction,or relative position from which the electricity comes, e.g., from the ACpower source. In complementary fashion, “downstream” or “in back of” or“behind” refers to the side, direction, or relative position away fromthe source, e.g., the direction in which the power goes away from acomponent, etc.

The first high voltage power switch 300 is preferably, but notnecessarily, a mechanical relay that is normally open, so power (currentthrough the relay coil) is required to close it. Also, once the powerswitch (relay) 300 is opened, it is preferred, although not essential,that the power switch 30 cannot be reset (closed) without some operatoror user intervention. In other words, when the temperature at the heaterrecedes, the relay switch 300 does not reset or close automatically.Instead, an operator or user has to actively do something to reset(close) the relay switch 300 in order to restart the controller 20 todeliver controlled power to the heaters. A mechanical relay switch ispreferred, although not essential, for the high-limit switch 300,because a solid state switch, such as a triac, has more resistance, thuswould produce more unnecessary heat and would be an unnecessary powerdrain.

A conventional latching relay device could perform the functionsdescribed above, but conventional latching relay devices that could beused in these kinds of heater control applications are large, bulkydevices that require a second coil and substantial power to operate.Therefore, an embodiment of this invention includes a high-limit controlcircuit 298 that is configured to cause an ordinary, normally openmechanical relay switch to remain open, even after the heatertemperature recedes below the upper temperature limit, until an operatoror user intervenes. Several example high-limit control circuits 298, onedigital and two analog, that enable an ordinary, normally openmechanical relay switch to function in this manner in the heater controlsystem 10 are included in this description.

An ordinary, normally open mechanical relay switch is a relay switchwith at least one set of electrical contacts that are spring biased toan open mode or position and a coil, which, when powered, generates amagnetic field or bias that overcomes the spring bias to close thecontacts. When the power to the coil is turned off so that no current ornot enough current flows through the coil to create a strong enoughelectromagnetic field or bias to overcome the spring bias, then thespring bias re-opens the contacts.

One example high-limit control circuit 298 for controlling thehigh-limit mechanical relay switch 300 to function as described aboveincludes a digital logic microprocessor or other logic circuit asindicated diagrammatically in the schematic circuit diagram of thecontroller 20 in FIGS. 28-31. In this example, the microprocessor orother digital logic circuit of the high-limit circuit 298, upon startup,is programmed to progress through a series of startup logic steps, whichinclude: (i) comparing the temperature sensed by the first (upper-limit)temperature sensor 52 to a preset high temperature limit, and (ii) ifthe sensed temperature does not equal or exceed the preset hightemperature limit, generating a signal to close the normally open relayswitch 300. For example, but not for limitation, the signal can beapplied to the gate of a low voltage, solid state switch, e.g., atransistor (not shown) to turn on a flow of low voltage DC electriccurrent through the coil of the mechanical relay switch 300 to cause itto close. If the sensed temperature does equal or exceed the preset hightemperature limit, the startup logic does not generate the signal thatwould cause the relay power switch 300 to close. Therefore, in oneexample implementation, if the relay power switch 300 is not closed, theDC power that powers the high-limit control circuit has to be turned offand then turned on again to make it go through its reboot or restartlogic when the sensed temperature does not exceed the preset hightemperature limit in order to close the relay power switch 300 after ithas been opened. Such turning off or removal of DC power to thehigh-limit control circuit 298 can be accomplished in a number of ways.For example, but not for limitation, since the DC power supply 294,which provides DC power to operate the high-limit control circuit 298 inthe example implementation in FIG. 8 is tapped into the AC power in theAC power leads 290, 292, the removal of DC power from the high-limitcontrol circuit 298 can be accomplished simply by unplugging ordisconnecting the controller 20 from the AC source power, which alsocuts off power to the DC power supply 294, thereby removing power fromthe high-limit control circuit 298. Then, reconnecting the controller 20to the AC source power will re-power the high-limit control circuit 298,thereby causing it to reboot and go through its startup logic again,which will close the relay power switch 300 if the startup logicdetermines that the sensed temperature does not equal or exceed thepreset high temperature limit, as explained above. Of course, other waysof turning the DC power to the high-limit circuit 298 on and off couldalso be provided, for example, a manually operated switch (not shown) infront of the DC power supply 294 or between the DC power supply 294 andthe high-limit circuit 298 could also be provided. A suitable logiccircuit for the high-limit control circuit 298 can include, for example,an ATmega168 microprocessor manufactured by Amtel Corporation, San Jose,Calif., although other integrated circuit chips that can be programmedto perform the described functions are readily available commerciallyand are well known to persons skilled in the art.

Again, a purpose of this example implementation is to require anoperator or user to actively intervene in order to restart a heater thathas been turned off by the upper-limit control circuit 298, and therebymake it more likely that the operator or user will check on the cause ofthe high-limit shutoff of the heater before turning it back on andleaving it unattended. At the same time, the use of the mechanical relayswitch 300 controlled in the manner described above, i.e., to open andshut off AC power to the heater in a reliable manner at or near apredetermined high temperature limit and then being closable again by asimple operator intervention, avoids the disadvantages of a thermal fusein the heater that either has to be replaced or renders the heaterunusable. It also avoids the disadvantages of a conventional latchingrelay, e.g., large, bulky, and a power drain, and it avoids thedisadvantages of a solid state switch, e.g., resistance, heatproduction, and power drain. Also, in the digital implementationdescribed above, the upper temperature limit or parameter is adjustable,which provides additional options and flexibility for users.

As persons skilled in the art know, there is little, if any, substantivedifference between a logic step that generates an action if a parameteris “equal to or greater than” a value or just “greater than” the value,other than the particular logic statement that the programmer chooses touse. Likewise, there is little, if any, substantive difference between alogic step that generates an action if a parameter is “equal to or lessthan” a value or just “less than” the value. In other words, forexample, if the logic step of the high-limit circuit is described orclaimed as generating a signal to open the relay 300 when the sensedtemperature equals or is greater than a preset upper temperature limitparameter, it is considered equivalent to generating a signal to openthe relay 300 when the sensed temperature exceeds, i.e., is greaterthan, the upper temperature limit parameter. Therefore, unless specifiedotherwise, >= is considered to be equivalent to > and vice versa, and <=is considered to be equivalent to < and vice versa.

As long as the temperature in the master heater 16 remains below thehigh temperature limit set in the high-limit control 298, the firstswitch remains closed, and the heaters 16, 16′ are controlled by theprocess control 296 in the controller 20 based on temperature signalsfrom the second temperature sensor 52 in the master heater 16, which canbe, for example, a thermocouple or thermistor. As shown in FIG. 28, thesignals from the second temperature sensor 52 are fed by the low voltagewires 58, 60 in the heater 16 and by a low voltage wire pair through theslave adapter cable 22 (FIG. 15) to an amplifier 306 in the controller20, where they are conditioned and amplified for use by the processcontrol 296.

Essentially, the process control 296 operates the second power switchassembly 302 to turn on and off the high voltage AC power to the heaters16, 16′ in order to maintain the temperature sensed by the secondtemperature sensor 52 within a predetermined range that is set in theprocess control 296, as is shown in more detail in FIG. 32. The switchassembly 302 in the example embodiment illustrated in FIG. 28 comprisestwo switches, e.g., a mechanical relay switch 303 and a solid statetriac switch 305, in parallel to minimize arcing and heat. The triac 305turns on just before, e.g., about 20 milliseconds before, the relayswitch 303 closes to minimize arcing in the relay switch 303 during theinitial closing of the contacts in the mechanical relay switch 303. Thetriac 305 then turns off, e.g., about 20 milliseconds after themechanical relay switch is closed, i.e., to avoid heat production in thetriac 305 while the relay switch 303 is closed and conducting thecontrolled AC power to the heaters 16, 16′. Then, the triac 305 turns onagain just before the relay switch 303 opens to minimize arcing in therelay switch 303 as it opens. These functions are controlled by theprocess control circuit 296, as is understood by persons skilled in theart. Mechanical relay switches and triac power switches are readilyavailable commercially in many sizes and configurations from numerousmanufacturers, as is well-known by persons skilled in the art.

The process control 296 also provides a number of other functions shownin more detail in FIG. 32, including, but not limited to, processinginformation to operate the display of, for example, green, amber, andred LED light displays 240, 242, 244, communicating information back andforth between the expansion module 202 and the base module 200, andreceiving signals from the high-limit control for processing fordisplays and output relating to the status of the first switch 300. Theprocess control circuit can also comprise an ATmega168 manufactured byAmtel Corporation, although myriad other microprocessors that could alsoserve these and other functions are well known and readily available topersons skilled in the art.

One of the functions provided by the process control 296 is processingtemperature input information for producing temperature range signals(sometimes also called “alert/alarm signals”) to be delivered to aremote monitoring location to confirm that the heater or heaters 16 areoperating within a desired temperature range. This function can serve anumber of uses. For example, if the heater temperature is outside of acertain desired operating range, which may or may not be related to thehigh temperature limit discussed above, this electronic temperaturerange signal can be used to trigger a mechanism (FIG. 27) for equipmentinterlock, i.e., preventing or interrupting an industrial process thatdepends on the heaters 16 operating properly to maintain the heat withina particular temperature range. Another use for such an electronictemperature range signal may be to generate a notice or alarm functionfor operators at a remote location to notify them that a heater or groupof heaters is outside of a desired operating range, i.e., either toocold or too hot. Of course, the uses for such an electronic temperaturerange or “out-of-range” signal are not limited to these examples.

To implement an electronic temperature range signal (also called“alert/alarm signal”) in this invention, an electronic relay device 310,which can be operated by the process control 296, is provided in thecontroller 20. A desired temperature range for the heater 16, eitherfactory-preset or user determined, is programmed into the processcontrol 296. The range can be set in absolute degrees or upper and lowerlimits, or it can be in incremental values around some operatingtemperature setting that can be either fixed or floating, depending onthe operator's requirements.

A low voltage, such as thirty (30) volts or less, supplied by a remotemonitoring device 15 (FIG. 27), is delivered to the controller 20 viathe low voltage wires 98, 100 and/or 102, 104 provided in the T-typesource power cable sections 26 and/or via the low voltage wires 118, 120in a terminated source power cable section 106, as explained above andshown in FIGS. 10-13, depending on whether the controller 20 is or isnot either the last controller 20 in a daisy chained series ofcontroller 20 or the only controller 20 in a system.

In the controller 20, one of the low voltage signal conductors is routedthrough the relay device 310, as shown by the traces 312, 314 in FIG.28, before it is routed back into the T-type source power cable 26 orterminated source power cable 106 (not shown in FIG. 28—see FIGS.12-13). A remote monitor device (FIG. 27) at the remote location 15 isconnected to the low voltage wires 98, 100 and/or 102, 104 in the T-typesource power cable 26 and/or 118, 120 in the terminated source powercable 106 for monitoring the voltage and/or current on these low voltagewires. For example, if all the relay devices 310 in all the controllers20 connected to the remote monitoring device at 15 via one or more ofthe T-type source power cables 26 or the terminating source power cable106 are closed, then a current will flow and/or the voltage will drop.On the other hand, if any one of the relay devices 310 in any of thecontrollers 20 is open, no current will flow in the low voltage lines inany of the source power cables 26, 106 and/or the voltage will be thehighest, i.e., the open circuit voltage that is applied to the lowvoltage wires by the remote monitoring device 15. Such voltage and/orcurrent conditions are monitored by the continuity detector 31 in theremote monitoring station 15, which can thereby detect whether all therelay devices 310 of all the controllers are closed, thus indicatingthat all of the heaters 16 are operating within the desired temperaturerange (closed signal circuit condition), or it can show that at leastone of the heaters 16 is not operating within the desired temperaturerange (open signal circuit condition). Therefore, it becomes apparentfrom this description why the last or only controller 20 in a daisychain connected series has to be connected to the remote monitoringdevice via terminated control power cable 106, as shown in FIGS. 12-13,and not with a T-type source power cable 26, as shown in FIGS. 10-11 and28. Specifically, if there is no controller 20 connected to the lastT-type source power cable 26, the low voltage signal circuit will alwaysbe open at the unconnected connector 112, e.g., unconnected wires 102,104 in FIG. 28, thus falsely indicating a heater 16 operating outsidethe desired range. The linear-type terminated source power cable 106prevents that problem, as shown in FIG. 29.

In summary, each controller 20 in a series that is daisy chain connectedwith the T-type source power cables 26 and the last controller 20 in theseries that is connected with the terminated source power cable 106, hasprogrammed in it a desired temperature operating range. As long as thecontrol process 296 of a controller 20 determines that its temperaturesensor 52 or both temperature sensors 50, 52 do not indicate atemperature outside the desired temperature range, the control processcircuit 296 keeps the relay device 310 closed. However, if thecontroller 20 determines from the sensed temperature information thatthe heater 16 is not operating within the desired temperature range, itwill open the relay device 310, thereby opening the low voltage signalcircuit, which is detectable by the continuity detector 31 at the remotemonitoring location 15. In response, the signal from the continuitydetector 31 can then trigger some alarm, notice, and/or control orinterlock signal for whatever purpose is desired, as discussed above.

As also discussed above and as can be seen in FIG. 28, the temperaturesensors 50, 52 in the master heater 16 are connected to the controller20 by the slave adapter cable 22, and the controller 20 uses signalsfrom those temperature sensors 50, 52 in master heater 16 in the processdescribed. However, even though the slave heaters 16′ are identical instructure to the master heater 16 in some embodiments, including havingthe same temperature sensors 50, 52, those temperature sensors 50, 52 ofthe slave heater 16′ are not connected to the controller 20. With no lowvoltage wires in the slave cable segment 128 of the slave adapter cable22, and no low voltage conductors in either the T-type slaved heatercable 24 or the terminated controlled power slave cable 184, thecontroller 20 does not get any temperature signals from the sensors 50,52 in the slave heaters 16′, which is what makes them function as slaveheaters 16′. Whatever the controller 20 determines to do, whether it isturning on and off the high voltage power, operating the temperaturerange relay 310, or other functions based on heater temperature, it isbased on the temperatures sensed by the sensors 50, 52 in the masterheater 16.

As mentioned above, all of the parameters needed by the high-limitcontrol 298 and the process control 296 to operate as described can bepreprogrammed or preset into the process control 296 and the high-limitcontrol 298, which is built in the base module 200 of the controller 20.However, if more control, functionality, monitoring, or othercapabilities are desired, such additional control functionality,monitoring or other capabilities can be provided in the expansion module202 that attaches to the base module 200. The example expansion module202 shown in FIG. 28 includes a display/adjust microprocessor 316, analpha-numeric display 204, user interface buttons 210, 212, 214, digitalcommunications input/output portals 222, 224, and a communicationsmicroprocessor 318. The display/adjust microprocessor 316 can also be anATmega168 manufactured by Amtel Corporation, although myriad othermicroprocessor circuits can also be used.

The display/adjust microprocessor 316 is connected to the user interfacebuttons 210, 212, 214, which can be used to retrieve and reset variousparameters and information, which the display/adjust microprocessor 316gets from, and inputs to, the process control 296 and/or the high-limitcontrol 298, which it also sends to the display 204. Such informationthat can be retrieved, displayed, and reset with the microprocessor 316can include, but is not limited to, desired operating temperature setpoint, high temperature safety limit, high temperature alert set point,low temperature alert set point, hysteresis, output PID (proportionalband, integral, and deviation), cycle time, ambient temperature (readonly), modbus device address, modbus band rate, and temperature units(Celsius or Fahrenheit). Other read only information such as baserelease version, base build number, interface release version, interfaceprototype version, and interface build number can also be retrieved anddisplayed.

The communications microprocessor 318 enables external datacommunications with a remote monitoring or control station, servicecomputers, and the like to input and output information, makeadjustments, modify programming, and the like, via the input/outputports 222, 224. The communications microprocessor 318 can be, forexample, a MAX3157 manufactured by Maxim Integrated Products, Sunnyvale,Calif., which has a transmitter and a receiver, although myriad othermicroprocessors could also be used for this function, as is known bypersons skilled in the art.

The schematic circuit diagram in FIG. 30 illustrates a heater 16connected directly to a controller 20, as is done in the multiple localheater control configuration of FIGS. 1-4. All of the connections andfunctionalities described for the controller 20, base module 200,process control 296, high-limit control 298, first switch 300, secondswitch 302, temperature range relay 310, heater 16, temperature sensors50, 52, heating element 32, expansion module 202 and other componentsare the same as explained above for FIG. 28, except that heater 16 isconnected directly to the controller 20. Therefore, there is no slaveadapter cable in this configuration, thus no slave heaters.

The schematic circuit diagram in FIG. 31 is also for a controller 20connected directly to a heater 16, thus no slave adapter cable and noslave heaters. Therefore, the circuit in FIG. 31 is the same as thecircuit in FIG. 30, except that it is either the last controller 20 in aseries or the only controller 20, so it has the terminated source powercable 106 instead of the T-type source power cable 26 for supplying thehigh voltage source power and the low voltage electronic temperaturerange circuit to that controller 20 shown in FIG. 31.

An example operating logic for implementing the present invention isshown in FIG. 32. The logic as well as the values and parameters in FIG.32 and used in this description are examples and not intended to belimiting. The illustrated logic starts in the upper-limit control 298.From start 320, a temperature measurement is taken from the first(high-limit) temperature sensor 50 at 322 and compared to the uppertemperature limit parameter. If the actual measured temperature from thehigh-limit temperature sensor 50 is less than the high-limit parameterin step 322, then the next step 324 tests whether that actualtemperature from sensor 50 is within 20° C. of the second (process)temperature sensor 52. This comparison 324 is done as a test todetermine if the temperature sensors 50, 52 are measuring reasonablyaccurate in relation to each other. If yes, then the temperature of thecontroller itself is measured at 326 to be sure it is not overheated,i.e., is less than 85° C. Overheating could occur, for example, if thecontroller 20 is too close to the heater 16, and it could damage theelectronic components in the controller 20. If the controller 20 isfound at 326 to not be overheated, then the high-limit control 298 keepsthe relay switch 300 closed, as indicated at 328, so that the highvoltage AC power remains available for control by the process control296 to power the heater(s) 16, 16′.

On the other hand, if any of the tests at 322, 324, 326 are negative,i.e., the sensed temperature is over the high temperature limit, thenthe high-limit control 298 opens the relay switch 300 at 330, whichinterrupts the AC power to the heater(s) 16, 16′. It also sends a signalto the process control 296 that indicates the relay switch 300 isopened, and, in response, the process control 296 activates an alarmsignal and/or flashes the appropriate (red) LED 240.

Continuing with the process control 296, a temperature measurement fromthe second (process) temperature sensor 52 is compared at 332 with theprogrammed set point (desired operating temperature) minus the sethysteresis parameter (e.g., about 3° C.). If the actual processtemperature measured by the process sensor 52 is at or below the setpoint minus hysteresis, then the actual temperature is compared at 334to the programmed low temperature alert (LTA) parameter, i.e., to seewhether the temperature is below the desired operating range. If thetemperature is at or below the LTA (e.g., about 20° C. below the setpoint temperature), then the process control 296 closes the second(process) switch 302 at 336 to provide AC power to the heater(s) 16,16′, and it turns on the output LED 244 (e.g., green) to indicate thatthe heater(s) 16, 16′ are turned on. On the other hand, if thetemperature at 334 is not at or below the low temperature alert (LTA)parameter, then the process switch (relay) 302 is closed as indicated at338, but the LED 242 (e.g., amber) is turned on to indicate that theactual process temperature is in the proper operating range.

If the comparison at 332 shows that the actual process temperaturemeasured by the process temperature sensor 52 is not at or below the setpoint minus the hysteresis, then the temperature is checked at 340 tosee if it is at or above the set point plus the hysteresis parameter. Ifit is, then the temperature is checked at 342 to see if it is at orabove the programmed high temperature alert (HTA) parameter (e.g., about20° C. above the set point temperature). If so, then the control relayswitch 302 is opened at 344 to turn off the AC power to the heater(s)16, 16′, and the “Alert/Alarm” LED (red) 240 is turned on.

On the other hand, if the temperature at 340 is not at or above setpoint plus hysteresis, then the temperature is within the controlhysteresis range, so the control relay switch 302 is kept open at 346pending changes in the thermal condition, and the “In Range” LED isturned on or left on.

If the temperature from the process temperature sensor 52 is not foundat 342 to be at or above the programmed HTA parameter, then the controlrelay switch 302 is open, as indicated at 348, and the “In Range” LED ison.

These and other functions are shown in the example drawings anddescribed above as being performed by several control processors, e.g.,296, 298, 316, 318. However, these functions and others can be performedby one or more processors in various combinations and with variousallocations of the functions among one or more microprocessors, as isunderstood by persons skilled in the art. Therefore, there can be moreor fewer processors than shown in the drawings to perform these examplefunctions.

Another example implementation of the high-limit control circuit 298 isillustrated in FIG. 33, wherein a switching positive temperaturecoefficient (PTC) thermistor semiconductor device is used for theupper-limit temperature sensor 50. Switching PTC thermistors aresemiconductor devices that exhibit a very small negative temperaturecoefficient of resistance until the device reaches a criticaltemperature, often referred to as the switch or transition temperature,whereupon the device exhibits sharp rise in the temperature coefficientof resistance as well as a large increase in resistance, e.g., aresistance change of as much as several orders of magnitude within atemperature span of a few degrees. Such switching PTC thermistors arereadily available commercially with transition temperatures in rangesfrom 60° C. to 160° C. and can be manufactured with transition or switchtemperatures at least as low as 0° C. and at least as high as 200° C.With the switching function inherent in the switching PTC thermistordevice used as the high-limit temperature sensor 50, the high-limitcontrol circuit 298 can be analog, as shown in FIG. 33, and stillprovide the desire features and functions of operating the normally openmechanical relay high-limit power switch 300 to open and shut off the ACpower to the heater(s), whenever the heater temperature equals orexceeds an upper temperature limit and then not close and turn on the ACpower again without an operator intervention or manual input when theheater temperature recedes below the upper temperature limit.

As shown in FIG. 33, the PTC thermistor temperature sensor 50 ispositioned in the heater 16 adjacent the AC powered heating element 32in order to sense temperatures caused by the heat produced by theheating element 32 as described above for the upper-limit temperaturesensor 52 in previously described example implementations shown in FIGS.9 and 27-30. The high-limit mechanical relay switch 300 is alsopositioned in the AC power circuit in the controller 20 to open andclose at least one of the AC power conductors, e.g., the AC powerconductor 290, as also described above and shown in FIGS. 27-30, so thatit shuts off the AC power to the heater 16 when the normally opencontact 307 is closed and turns off the AC power to the heater 16 whenthe normally open contact 307 is open. The other AC power conductor 292passes through the controller 20 to the outlet connector 142, where itconnects with the switched AC power conductor 290 to the heater 16, asdescribed above.

The switching PTC thermistor used as the high-limit temperature sensor50 is connected in series with a rectifier circuit 307 that powers thecoil of the relay switch 300 so that current has to flow through theswitching PTC thermistor of the temperature sensor 50 in order to powerthe coil to close the normally open contact 307 of the relay switch 300,i.e., to turn on the AC power to the heater 16. Therefore, in normaltemperature operation, i.e., when the temperature sensor 50 is under theupper temperature limit, which is set by the switching or transitiontemperature of the PTC thermistor of the temperature sensor 50, the PTCthermistor has a low resistance that easily conducts enough AC currentthat, when rectified, flows through the coil of the relay switch 300 tocreate the magnetic field required to close the contact 307.Consequently, in such normal temperature operation, the AC power circuitin the controller 20, comprising the AC power conductors 290, 292, isclosed and can conduct AC power to the heater 16, subject, of course, tothe closed or open status of the process relay switch arrangement 302,as described above. However, if the temperature of the switching PTCthermistor of the high-limit temperature sensor 50 rises to or exceedsits switching or transition temperature, its resistance increasessharply and effectively turns off the rectified current to the coil ofthe relay switch 300, thereby allowing the normally open contacts 307 toopen and the normally closed contacts 308 to close. Consequently, theopen contacts 307 opens the AC power circuit of AC conductors 290, 292,thereby turning off the AC power to the heater 16. Rectifier circuits,for example, full-wave bridge rectifier circuits, are well known topersons skilled in the art, thus need no further description for anunderstanding of this circuit.

Then, when the temperature of the PTC thermistor of the upper limittemperature sensor 50 recedes back down to a temperature below the hightemperature limit, i.e., below the switching or transition temperatureof the PTC thermistor, and the current then again flows through the PTCthermistor, the high-limit control circuit 298 still prevents the coilof the relay 300 from re-closing the contacts 307 to turn the AC powerback on to the heater 16 until there is an operator intervention. In theexample upper-limit control circuit 298 shown in FIG. 33, there is adrain circuit comprising a switch 309, e.g., a triac as shown in FIG. 33or other solid state or mechanical relay switch, and a drain resistor311 connected parallel to the rectifier circuit 301 and coil of therelay switch 300. The drain resistor 311 has much less impedance thanthe coil of the relay switch 300, for example, an order of magnitudeless, so that when the triac or other relay switch 309 is turned on, thecurrent that flows through the PTC thermistor of the temperature sensor50 is drained away from the rectifier 301 and coil of the relay 300,which prevents the coil from generating the electromagnetic field thatis necessary to close the contacts 307 in the relay switch 300.

The triac 309 is turned on by the AC current that flows through the PTCthermistor of the temperature sensor 50, which is applied to the gate313 of the triac 309 via the normally closed contacts 308 of the relayswitch 300. Therefore, when the PTC thermistor of the temperature sensor50 turns off the rectified current to the coil of the relay switch 300upon the occurrence of a high temperature event at the heater 16, thenormally open contacts 307 in the relay switch 300 open to turn off theAC power to the heater 16, as described above, and the normally closedcontacts 308 close, as shown in FIG. 33, to apply the AC power to thegate 313 of the triac 309 to activate (close) the drain circuit.Consequently, when the temperature at the heater 16 recedes so that thetemperature of the PTC thermistor of the temperature sensor 50 fallsbelow its switching or transition temperature and again conductscurrent, the current is diverted away from the coil of the relay switch300 and is instead drained through the drain resistor 311. With thecurrent conducted by the PTC thermistor being drained away from the coilof the relay switch 300, the coil cannot create the electromagneticfield required to close the normally open contacts 307, so the AC powerto the heater 16 remains turned off, even though the temperature at thePTC thermistor of the temperature sensor 50 has receded, and it is againconducting electric current.

To turn the AC power back on to the heater 16, therefore, a manuallyoperated switch 315 is provided to break or open the gate power circuitand thereby to turn off the triac 309. As soon as the triac 309 isturned off by the manually operated switch 315, the drain circuitthrough the drain resistor 311 is deactivated, so the current from thePTC thermistor of the temperature sensor 50 again is rectified by therectifier circuit 301 and flows through the coil of the relay switch300. Therefore, the coil creates the electromagnetic field required toopen the contacts 308 and to close the contacts 307 to therebyreactivate the AC power to the heater 16 and to remove the AC power fromthe gate circuit. Consequently, when the manually operated switchreturns to the closed mode, the triac 309 does not turn back on, becausethe current from the PTC thermistor keeps the contacts 308 open as longas the temperature at the temperature sensor 50 remains below theswitching or transition temperature of the PTC thermistor. For thereasons described above, therefore, the provision of the drain circuit,which is disabled by the manually operated switch 315, an operatorintervention, i.e., to operate the switch 315, is required to reactivateAC power to the heater 16 after it has been turned off due to a hightemperature event in the heater 16 that equals or exceeds the switchingor transition temperature of the PTC thermistor of the high-limittemperature sensor 50.

It should be noted that it is primarily heat from an external source,e.g., heat from the heating element 32 or from hot purge or other gasesor liquids in the pipe itself, that causes the temperature of the PTCthermistor in this example implementation to rise to its switching ortransition temperature to turn off the AC power to the heater 16. Incontrast, temperature rises in PTC thermistors used in conventionalthermal fuse or thermal circuit breaker applications are causedprimarily by I²R heat generated internally in the PTC thermistors. Inother words, PTC thermistors have inherent resistance (R) to currentflow (I), and excessive current (I) flow in the PTC thermistor willcause substantial heat production in the PTC thermistor itself, and, ifthe temperature reaches the transition or switching temperature, the PTCthermistor will substantially shut off current flow.

Any of a variety of status signals from the high-limit circuit 298 canbe provided to the process control circuit 296 for use in generatingstatus and/or alert/alarm signals, or for use in process logic, and thelike. For example, but not for limitation, a sensor 317, such as acurrent detector, can be used to indicate that the relay switch 300 isactivated to provide AC power to the heater 16 or deactivated to shutoff AC power to the heater 16. Also, for example, but not forlimitation, a sensor 319, such as a current detector, can be used toindicate whether the temperature at the high-limit temperature sensor 50is either (i) below the switching or transition temperature of the PTCthermistor, i.e., current is detected, or (ii) at or above the switchingor transition temperature of the PTC thermistor, i.e., current is notdetected. These and other status signals can be used by the processcontrol circuit 296, for example, to generate status and/or alert/alarmsignals to the LED display 321 and/or to the display/adjustmicroprocessor 316.

Another example implementation of the high-limit control circuit 298utilizing a PTC thermistor for the high-limit temperature sensor 50 isshown schematically in FIG. 34. In this example implementation, thetriac 309 of the FIG. 33 example is replaced by a second switchmechanism 325 in the relay switch 300′, which is normally closed and isactivated by the same coil that activates the first or primary switchmechanism 323 of the relay switch 300′. This second switch 325 couldalso be provided by a separate relay switch (not shown), but dual switchrelays, such as the dual switch relay 300′ shown schematically in FIG.34 are readily available and more compact than two separate relayswitches. In this FIG. 34 example, the relay switch is labeled 300′instead of 300, not for limitation, but only to distinguish this examplerelay switch 300′ from the previously described relay switch 300. Inother words, while the primary function of both of these example relayswitches 300, 300′ is to turn the AC power to the heaters off if thereis a high temperature event, the relay switch 300′ has the additionalsecond switch 325 for the drain circuit in this implementation.

In the FIG. 34 example, the contact 307 of first switch 323 in the relay300′, which turns on and off the AC power to the heater 16, is normallyopen, as is the contact 307 of the FIG. 33 example, so current has toflow through the coil of the relay 300′ to close the contact 307 so thatthe AC power can be provided to the heater 16, subject, of course, tothe opening and closing of the process switch assembly 302 as describedabove. The coil of the relay 300′ is powered by rectified currentderived by the rectifier 301 from AC current that flows through the PTCthermistor of the high-limit temperature sensor 50 whenever thetemperature of the PTC thermistor is below its switching or transitiontemperature, which defines the upper temperature limit. However, if thetemperature at the temperature sensor 50 reaches or exceeds theswitching or transition temperature of the PTC thermistor, the currentflow through the PTC thermistor, thus also the rectified current throughthe coil of the relay 300′, is stopped. With no current flow through thecoil, the normally open first switch 323 opens the contacts 307, therebyturning off the AC power to the heater 16, and the normally closedsecond switch 325 closes the contacts 308′, thereby closing oractivating the drain circuit comprising the drain resistor 311.

When the temperature at the temperature sensor 50 recedes below theswitching or transition temperature of the PTC thermistor so that itagain conducts electric current, the closed drain circuit drains thecurrent through the drain resistor 311, thereby depriving the coil ofthe relay 300′ of the current required to re-close the AC power (first)switch 323. Again, as mentioned above, the drain resistor 311 has muchsmaller resistance than the coil, so, when the drain circuit is closed,the current will flow preferentially through the drain circuit insteadof through the coil, which is connected electrically in parallel to thedrain circuit. Therefore, even though the temperature at the temperaturesensor 50 has receded below the upper temperature limit, the draincircuit prevents the relay 300′ from providing AC power to the heater16.

To restore AC power to the heater 16, an operator can open the draincircuit with the manually operated switch 315. By even momentarilyopening the manually operated switch 315, the drain circuit isdeactivated, so rectified current is restored to the coil of the relay300′. With current flowing again through the coil, the contacts of thefirst switch 323 close to turn on the AC power to the heater 16, and thecontacts of the second switch 325 open to disable the drain circuit.Therefore, when the manually operated switch closes again, the draincircuit stays deactivated.

The manually operated switch 315 can be any of a variety of switchtypes, but the normally closed, push button switch illustratedschematically in FIGS. 33 and 34 is a convenient example switch type forthis application. Depression of the button 327 causes the switch 315 tomomentarily open. Then, when manual force is removed from the button327, the spring 329 re-closes the switch.

While the embodiments of the invention described above have the sourcepower and signal circuit distributions made with cables sections, e.g.,the T-type source power cable 26 with its branch 85 branching from thetrunk 83 (FIG. 10), the slave cable adapter 22 with its slave cablesegment 128 branching away from its master cable segment 126 (FIG. 14),and the T-type controlled power cable 24 with its branch 163 branchingaway from its trunk 161 (FIG. 16), these distributions can also be madewith junction boxes. For example, but not for limitation, the functionof the slave cable adapter 22 can also be provided by the slave adapterjunction box 322 shown in FIGS. 35-37 and illustrated in use position inthe schematic circuit diagram of FIG. 38 for a single point controlsystem with two slave heater branches controlled by a single controller20.

The slave adapter junction box 322 has a housing 324 with an inletconnector 330 and a master outlet connector 332 in opposite top andbottom walls 325, 326, of the housing 324 and two slave outletconnectors 333, 334 in opposite lateral side end walls 327, 328 of thehousing 324. The inlet connector 330, like the inlet connector 130 ofthe slave adapter cable 22, is configured to mate with the outletconnector 142 of the controller 20 (FIG. 20). The master outletconnector 332, like the master outlet connector 132 of the slave adaptercable 22, is configured to mate with the heater input connector 64 onthe heater cord 62 of a heater 16. Therefore, the pair of powerconductor leads 336, 338 carry controlled power from the controller 20to the master heater 16, while the two pairs of signal conductors 340,342 and 344, 346 carry signals from the high-limit temperature sensor 50and the process temperature sensor 52, respectively, to the controller20.

The two slave outlet connectors 333, 334 of the slave adapter junctionbox 322 are configured the same as the slave outlet 134 of the slaveadapter cable 22 so that they can mate with the inlet connectors 172 ofthe T-type slave controlled power cables 24 and the inlet connectors 190of the linear-type terminating controlled power slave cables 194. Onepair of power conductors 348, 350 connect the outlet connector 333electrically in parallel to the controlled power conductors 336, 338,and another pair of power conductors 352, 354 connect the outletconnector 334 electrically in parallel to the controlled powerconductors 336, 338.

When the slave adapter junction box 322 is connected to the controller20, as shown in FIG. 38, with one heater 16 connected to the masteroutlet connector 332 and other heaters 16′ connected into the slaveoutlet connectors 333, 334, the slave adapter junction box enables theheater that is connected to the master outlet connector 332 to functionas the master heater 16 and disables the temperature sensors 50, 52 ofthe heaters that are connected to the slave outlet connectors 333, 334so that those heaters function as slave heaters 16′. Therefore, thecontroller receives temperature information from the master heatersensors 50, 52 and uses it to provide controlled power to the heatingelements 32 of both the master heater 16 and the slave heaters 16′.

There can, of course, be more than two slave outlet connectors in theslave adapter junction box 322 to accommodate more than two daisy chainconnected series of slave heaters. Also, while it is not shown in thedrawings, split slave cables or additional junction boxes can beconnected to the slave outlet connectors 333, 334 of the slave adapterjunction box or to the slave outlet connector 134 of the slave adaptercable 22 to power additional daisy chain connected series of slaveheaters 16′ if desired or needed.

A source power junction box, for example, the source power junction box350 shown in FIGS. 39-42, can be used in place of the T-type sourcepower cable 26 in the assemblies shown in FIGS. 1-8. In the examplesource power junction box 350, a source power junction branch outletconnector 352 protrudes from the bottom surface 354 of the source powerjunction box 350 and is configured for mating connection to the inletconnector 140 of the controller 20 (FIGS. 20 and 21) so that the sourcepower junction box 350 can be mounted directly on the controller 20 byplugging the source power junction branch outlet connector 352 to theinlet connector 140.

A source power junction inlet connector 356 on a first lateral sidesurface 358 of the source power junction box 350 receives source powerinto the source power junction box 350 from, for example, a source powerextension cable 25 as described above in relation to FIG. 27 and shown,for example, in FIG. 42. Therefore, the source power junction inletconnector 356 in FIGS. 39 and 40 can be configured the same as the inletconnector 82 of the T-type source power cable 26 for substitutablemodular connectivity to the AC power source 13 (FIG. 27).

A trunk outlet connector 360 on a second lateral side surface 362 of thesource power junction box 350 in FIGS. 39 and 40 is provided for daisyconnection of one or more additional controllers 2, as shown in FIG. 42,and can be configured the same as the trunk outlet 86 of the T-typesource power cable 26 (FIGS. 1-8) for substitutability with the T-typesource power cable 26. Therefore, any of the following can be pluggedinto the trunk outlet 360 of the source power junction box 350: (i)another source power extension cable 25; (ii) a T-type source powercable 26; or (iii) a linear-type terminating source power cable 108.

An example schematic circuit diagram for the example source powerjunction box 350 is shown in FIG. 41. A pair of trunk source powerconnectors 364, 366 extends uninterrupted from the inlet connector 356to the trunk outlet connector 360, and a pair of source power branchconductors 368, 370 extend from a parallel connection with the trunksource power conductors 364, 366 to the branch outlet connector 352.Therefore, the branch outlet connector 352 is connected electrically inparallel to the source power conductors in relation to the trunk outletconnector 360.

The branch outlet connector 352 is connected electrically in series,however, between the inlet connector 356 and the trunk outlet connector360 with respect to the signal circuit conductors in the source powerjunction box 350. Therefore, as shown in FIG. 41, one of the signalcircuit conductors, e.g., the trunk signal circuit conductor 372,extends straight through the junction box 350 from the inlet connector356 to the trunk outlet connector 360. The other signal circuitconductor comprises an inlet branch signal circuit conductor 374extending from the inlet connector 356 to the branch outlet connector352 and an outlet branch signal circuit conductor 376 extending from thebranch outlet connector 352 to the trunk outlet connector 360.

Therefore, while a plurality of controllers 20 can be daisy chainconnected electrically in parallel via the power source junction box 350to the AC power source 13 (FIG. 27), as shown in FIG. 42, they will beconnected electrically in series via the power source junction box 350to the signal circuit 23 (FIG. 27) in the same manner as described abovefor the T-type power source cables 26. Of course, any number of sourcepower junction boxes 350 can be daisy chain connected together, withsource power extension cables 25, as shown in FIG. 42, for any number ofcontrollers 20.

Another example power source junction box 380 illustrated in FIGS. 43and 44 has more than one trunk outlet. For example, but not forlimitation, in addition to the inlet connector 384 and the branch outletconnector 382, which are substantially the same as the inlet connector354 and branch outlet connector 352 described above for the junction box350, the power source junction box 380 is shown in FIGS. 43 and 44 withtwo trunk outlet connectors 386, 388 in respective opposite sides 387,389. Both of the outlet connectors 386, 388 are configured the same fordaisy chain connectivity to additional power source extension cables 25,T-type source power connectors 26, and linear-type terminating sourcepower cables 108 so that two separate daisy chain connected sets ofcontrollers (not shown) can be connected to the AC power source 13 andto the signal circuit 23 via the source power junction box 380.

As shown in the example schematic circuit diagram in FIG. 45 for theexample power source junction box 380, the trunk source power conductorpairs 390, 392, 394 and the branch source power conductor pair 396connect both of the trunk outlet connectors 386, 388 and the branchoutlet connector 382 electrically in parallel to the inlet connector384. The signal circuit conductors 398, 400, 402, 403, however, connectthe trunk outlet connectors 386, 388 and the branch outlet connector 382electrically in series to the inlet connector 384.

Of course, more than two trunk outlet connectors can be provided in thesource power junction box 380, if desired, with substantially the samekinds of parallel source power and series signal circuit conductorconnections as described above for each additional trunk outletconnector. Also, if desired, the branch outlet connector 382 could beeliminated so that the junction box 380 would then function only toconnect a plurality of daisy chain connected series of controllers (notshown) to an AC power source 15 and to a signal circuit 23, but it wouldnot be connectable directly to a controller inlet connector 140 withoutan intervening T-type source power cable 26, an intervening linear-typeterminating source power cable 108, or a source power extension cable 25(if the inlet connector 140 is configured for connection of a sourcepower extension cable 25 as discussed above).

A conventional connector latch feature on some commercially availableconnectors, such as Molex™ connectors include a latch lever, such as thelatch lever 410 shown on the male connector 78 in FIG. 46, with a dog412 on its distal end that is sized and shaped to engage a latchprotrusion on the female connector, such as the protrusion 414 shown onthe controller inlet connector 140 in FIG. 47. Such engagement of thelatch protrusion 414 by the dog 42 on the latch lever 410 is intended tosecure the male connector to the female connector until it is disengagedby pivoting the latch lever 410 on an elastic hinge 416, as shown inFIG. 48, which releases the male connector from the female connector andallows them to be disconnected or unplugged from each other. However, insome applications, such conventional latches are not secure enough, andit is too easy for the connectors to be unplugged unintentionally, forexample, by bumping or rubbing past them in tight spaces, and the like.

Therefore, to provide further security and resistance to unintentionaldisconnection of the connectors, for example, of the connectors 78, 140shown in FIGS. 46-48, a cantilevered resilient spring biasing tab 420 ispositioned adjacent the distal end 418 of the latch lever 410. Thebiasing tab 420 bears against the distal end 418 of the latch lever 410and has a resilient spring bias force that resists movement of the latchlever 410 in a manner that would disengage the dog 412 from the latchprotrusion 414. However, when a user forces the latch lever 410 to pivotabout the elastic hinge 416, which also acts as a fulcrum for the latchlever 410, as indicated by pivot arrow 422, the distal end 418 of thelatch lever 410 pushes outwardly against the spring bias force of thebiasing tab 420 and forces the biasing tab 420 to pivot outwardly, asindicated by pivot arrow 424 in FIG. 48. The elastic resilient springbias of the tab 420 does yield under enough force to allow the dog 412on the latch lever 410 to disengage from the latch protrusion 414 sothat the branch outlet connector 78 can be unplugged from the controllerinlet connector 140.

There are myriad ways to provide a spring biasing force to bear on thelatch protrusion 414. One example implementation of this feature is tomold the biasing tab 420 as cantilevered part of the housing 201 of thebase unit 200, as illustrated in FIGS. 46-48. Depending on how much biasforce or how yieldable a particular application requires for the tab420, a portion of the housing 201 at the cantilevered joint of the tab420 to the rest of the housing 201 can be thinner to function as aresilient elastic hinge 426, as shown in FIGS. 47 and 48. A slot 428 canbe provided in the housing to accommodate movement of the latch lever410 into and out of the housing 201. A tapered cam surface 421 can beprovided on the tab 420 to facilitate camming the tab 420 out of the waywhen the latch lever 410 is being inserted into the housing 201 as theoutlet connector 78 is plugged into the inlet connector 140.

As mentioned above, this bias force feature can also be implemented inother ways. Several examples are shown in FIGS. 49-51. In FIG. 49, thebiasing force is provided by a compressible leaf spring 430 mounted in abracket 432 on the inside of the housing 201. In FIG. 50, a coilcompression spring 434 provides the bias force, and, in FIG. 51, anelastically compressible material 436, such as rubber, silicon rubber, afoamed elastomer, or other foamed material is shown to provide the biasforce against the distal end 418 of the lever 410.

While the biasing tab 420 has been described above in relation to thebranch outlet connector 78 and the controller inlet connector 140, it isalso applicable to the controller outlet connector 142 and whateverinterfacing inlet connector is plugged into the controller outletconnector, e.g., the heater inlet connector 64, slave adapter inletconnector 130, slave junction box inlet connector 330, etc., asdescribed above. It can also be used in relation to the slave junctionbox outlet 322, as indicated by tab 420′ in FIGS. 35 and 36.

Since these and numerous other modifications and combinations of theabove-described method and embodiments will readily occur to thoseskilled in the art, it is not desired to limit the invention to any ofthe exact construction and process shown and described above. While anumber of example aspects and embodiments have been discussed above,those of skill in the art will recognize certain modifications,permutations, additions, and sub-combinations thereof. It is thereforeintended that the following appended claims and claims hereafterintroduced are interpreted to include all such modifications,permutations, additions, and sub-combinations as are within their truespirit and scope. The words “comprise,” “comprises,” “comprising,”“has,” “have,” “having,” “include,” “including,” and “includes” whenused in this specification and in the following claims are intended tospecify the presence of stated features or steps, but they do notpreclude the presence or addition of one or more other features, steps,or groups thereof.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. Heater control apparatusfor controlling power to a heater that has an AC powered heating elementwhich produces heat when connected to an AC power source, said heatercontrol apparatus comprising: A. A first temperature sensor and a secondtemperature sensor positioned in close enough proximity to the heatingelement to sense heat produced by the heating element; B. A heatercontroller comprising: (i) an AC power circuit extending between aninlet connector in the heater controller and an outlet connector in theheater controller, wherein said inlet connector is connectableelectrically to an AC power source and said outlet connector isconnectable electrically to the heating element to provide AC power tothe heating element via the AC power circuit; (ii) a high-limit powerswitch in the AC power circuit between the inlet connector and theoutlet connector of the heater controller that is capable of opening andclosing the AC power circuit; (iii) a high-limit control circuit that isconnected to the high-limit power switch in a manner that causes thehigh-limit power switch to open the AC power circuit in response to atemperature sensed by the first temperature sensor exceeding ahigh-limit temperature parameter and that causes the high-limit powerswitch to close in response to the temperature sensed by the firsttemperature sensor not exceeding the high-limit temperature parameterand a power sequence condition; (iv) a controllable process power switchin the AC power circuit between the inlet connector and the outletconnector of the heater controller that is capable of opening andclosing the AC power circuit to control the AC power provided at saidoutlet; and (v) a process control circuit that is connected to theprocess power switch in a manner that causes the process power switch toopen and close the AC power circuit in response to comparison of thetemperature sensed by the second temperature sensor with a presetdesired set point temperature.
 2. The heater control apparatus of claim1, wherein the controllable power process switch is positioned in serieselectrically with the high-limit power switch.
 3. The heater controlapparatus of claim 2, wherein the controllable power process switch ispositioned electrically in series between the high-limit switch and theoutlet of the heater controller.
 4. The heater control apparatus ofclaim 1, wherein the power sequence condition includes opening a draincircuit that, when closed, prevents the high-limit power switch fromclosing.
 5. The heater controller apparatus of claim 1, wherein thepower sequence condition includes a sequence comprising power to theprocess control circuit being terminated and then reestablished.
 6. Theheater controller apparatus of claim 5, wherein the high-limit controlcircuit is programmed to cause the high-limit power switch to open andthereby turn off AC power to the outlet connector if the temperaturesensed by the first temperature sensor is higher than the high-limittemperature parameter.
 7. The heater control apparatus of claim 6,wherein the high-limit control circuit is programmed to cause thehigh-limit power switch to close if the temperature sensed by the firsttemperature sensor is not higher than the high-limit temperatureparameter and the power sequence condition has occurred.
 8. The heatercontrol apparatus of claim 1, wherein the process control circuit isprogrammed to cause the process power switch to open the AC powercircuit if the temperature sensed by the second temperature sensorexceeds a preset hysteresis upper value in relation to a preset desiredset point temperature and to close the AC power circuit if thetemperature sensed by the second temperature sensor is below the presethysteresis lower value in relation to the preset desired set pointtemperature.
 9. The heater control apparatus of claim 7, wherein theheater controller also has a DC power supply connected electrically tothe AC power circuit between the inlet connector of the heatercontroller and the high-limit power switch for converting AC power to DCpower and providing the DC power to the high-limit control circuit, andwherein the power sequence condition includes the DC power to thehigh-limit control circuit being terminated and then reestablished. 10.The heater control apparatus of claim 1, wherein the high-limit powerswitch comprises a mechanical relay switch that opens and closes inresponse to signal input from the high-limit control circuit.
 11. Theheater control apparatus of claim 1, wherein the process power switchcomprises a solid state power switch that turns off and on to open andclose the AC power circuit in response to signal input from the processcontrol circuit.
 12. The heater control apparatus of claim 11, whereinthe solid state power switch includes a triac.
 13. The heater controlapparatus of claim 1, including: (i) a temperature range signal circuitin the heater controller connected to the inlet connector for connectionto a remote temperature range signal circuit; and (ii) a temperaturerange signal switch in the heater controller that opens and closes thetemperature range signal circuit in response to temperature range signalinput from the process control circuit.
 14. The heater control apparatusof claim 13, wherein the process control circuit is programmed tocompare the temperature sensed by the second temperature sensor to apreset desired operating temperature range and to generate thetemperature range signal input to the temperature range signal switch tocause the temperature range signal switch to open the temperature rangesignal switch if the temperature sensed by the second temperature sensoris not within the preset desired operating temperature range and toclose the temperature range signal switch if the temperature sensed bythe second temperature sensor is within the preset desired operatingtemperature range.
 15. The heater control apparatus of claim 1, wherein:(i) the high-limit control circuit is capable of being programmed withthe high-limit temperature parameter and of receiving program signalsfor adjusting the high-limit temperature parameter; and (ii) the processcontrol circuit is capable of being programmed with the desired setpoint temperature and the hysteresis and of receiving program signalsfor adjusting the set point temperature and the hysteresis.
 16. Theheater control apparatus of claim 15, including a base control modulehousing that contains the AC power circuit, the high-limit switch, thehigh-limit control circuit, the process power switch, the processcontrol circuit, the inlet connector, and the outlet connector.
 17. Theheater control apparatus of claim 16, including an expansion modulehousing that contains a tactile data input interface connectedelectronically to an adjust/display microprocessor for inputtingadjustment data for adjusting the high-limit temperature parameter, thedesired set point temperature, the hysteresis, and the desired operatingtemperature range to the adjust/display microprocessor, a visualalpha-numeric display connected electronically to the adjust/displaymicroprocessor for receiving electronic data signals from theadjust/display microprocessor for visual display, and an electronic dataport with contacts for interfacing the adjust/display microprocessorelectronically to the base module, and wherein the expansion modulehousing is physically attachable to the base module housing in adetachable manner with the contacts of the electronic data port of theexpansion module in mating alignment with complementary contacts of acorresponding electronic data port on the base module housing, saidadjust/display microprocessor being programmed to process input datasignals from the tactile data input interface for delivery of queriesand adjustments to the high-limit control circuit and to the processcontrol circuit and for receiving and processing data from thehigh-limit control circuit and from the process control circuit fordisplay, whereby attachment of the expansion module housing to the basemodule housing enables user input of adjustments of the presethigh-limit temperature parameter, set point temperature, hysteresis, anddesired operating temperature range as well as display of the presethigh-limit temperature parameter, set point temperature, hysteresis, anddesired operating temperature range.
 18. The heater control apparatus ofclaim 517 wherein the expansion module also includes a communicationsport for receiving adjustment data from an external data generatingdevice for adjusting the high-temperature parameter and the operatingtemperature set point, and a communications microprocessor withelectronic connections to the communications port and to theadjust/display microprocessor, said communications microprocessor beingprogrammed for feeding the received data to the adjust/displaymicroprocessor, which is programmed for processing and sending thereceived data to the high-limit control circuit and the process controlcircuit.
 19. The heater control apparatus of claim 18, wherein thecommunications microprocessor is also programmed for receiving andprocessing data from the high-limit temperature parameter data and theoperating temperature set point, which are processed by theadjust/display microprocessor for transmission via the communicationsport to an external display.
 20. The heater control apparatus of claim17, wherein the process control circuit is also programmed to comparethe temperature sensed by the second temperature sensor to a presetdesired temperature operating range and to generate one or more of aplurality of status signals that indicate: (i) that the process controlcircuit has the AC power circuit turned on, i.e., in “output” mode; (ii)that the temperature sensed by the second temperature sensor is withinthe desired operating temperature range, i.e., “in range”; and (iii)that the temperature sensed by the second temperature sensor is notwithin the desired operating temperature range, i.e., “alert/alarm”. 21.The heater control apparatus of claim 20, including a LED display in thebase module that comprises a plurality of LEDs, individual ones of whichlight in response to respective ones of the status signals.
 22. Theheater control apparatus of claim 21, wherein the expansion modulehousing includes a front panel, a rear panel, and a plurality of lightconductors that extend from the back panel to the front panel and thatalign with respective ones of the LEDs when the expansion module isattached onto the base module so that the light conductors conduct lightfrom respective ones of the LEDs to the front panel of the expansionmodule for visual displays of the “output”, “in range”, and“alert/alarm” status.
 23. Heater control apparatus, comprising a set ofcomponents that are configured for assembly in a variety of desiredcombinations of daisy chain connected heater control systems for aplurality of heaters, including: A. A plurality of heater controllerbase modules, each of which includes a base module housing containing(i) an AC power circuit extending between an inlet connector and anoutlet connector in the base module housing, (ii) a controllablehigh-limit power switch and a process power switch in the AC powercircuit, (iii) a high-limit control circuit that controls the high-limitpower switch to turn the AC power circuit on and off to the outletconnector in response to a comparison of a temperature measurement froma first temperature sensor to a preset high-temperature parameter and apower sequence that includes a power off and on sequence, and (iv) aprocess control circuit that controls the process power switch to turnthe AC power circuit on and off to the outlet connector in response to acomparison of a temperature measurement from a second temperature sensorto a preset operating set point temperature; B. A plurality ofcontroller expansion modules, each of which includes an expansion modulehousing that is physically attachable to the base module and contains(i) a tactile data input interface, (ii) a visual alpha-numeric display,(iii) an adjust/display microprocessor, and (iv) a data connectioninterface with the base module for user input of adjustments of thehigh-limit parameter and the operating temperature set point and fordisplay of the high-limit parameter and the operating temperature setpoint; C. A plurality of heaters, each of which comprises (i) an ACpowered heating element for producing heat, (ii) a first temperaturesensor positioned in close enough proximity to the heating element tosense heat produced by the heating element, (iii) a second temperaturesensor positioned in close enough proximity to the heating element tosense heat produced by the heating element, and (iv) a heater inletconnector that is connected electrically to the heating element and tothe first and second temperature sensors and which is physically andelectrically for mating connection to the outlet connector of the heatercontroller for routing controlled AC power from the AC power circuit inthe heater controller to the heating element of the heater and forrouting sensed temperature signals from the first and second temperaturesensors to the heater controller; D. A plurality of T-type source powercables, each of which comprises (i) a trunk section and a branchsection, (ii) a trunk inlet connector and a trunk outlet connector onopposite ends of the trunk section, (iii) a branch outlet connector onthe branch section that is configured physically and electrically formating connection to the inlet connector of the heater controller forrouting AC source power into the heater controller, and (iv) a pair oftrunk AC power conductors that extend between and connect the trunkinlet connector electrically to the trunk outlet connector, and whereinsaid branch outlet connector being connected electrically in parallel tothe trunk AC power conductors, wherein the trunk inlet connector and thetrunk outlet connector are configured physically and electrically formating connection with each other so that the trunk sections of theplurality of T-type source power cables can be daisy chain connectedtogether in order to provide AC source power from an AC power source tothe plurality of heater controllers; E. At least one linear-typeterminating source power cable with an inlet connector and a terminaloutlet connector on opposite ends of the linear-type terminating sourcepower cable and a pair of AC power conductors extending between andelectrically connecting the inlet connector and the terminal outletconnector, wherein the inlet connector of the linear-type terminatingsource power cable is configured physically and electrically for matingconnection to the trunk outlet connector of the T-type source powercable and the terminal outlet connector of the linear-type terminatingsource power cable is configured physically and electrically for matingconnection with the inlet connector of the heater controller for routingthe AC source power to the heater controller; F. A slave adaptercomprising (i) a master segment that includes a master inlet connector,which is configured physically and electrically for mating connectionwith the outlet connector of the heater controller for routingcontrolled AC power from the heater controller to the slave adapter andfor routing temperature signals from the first and second temperaturesensors to the heater controller, a master outlet connector, which isconfigured physically and electrically for mating connection with theheater inlet connector for routing controlled AC power from the slaveadapter to a master heater and for routing temperature signals from thefirst and temperature sensors to the slave adapter, a pair of master ACpower conductors that extend between and electrically connect the masterinlet connector to the master outlet connector to conduct controlled ACpower from the master inlet connector to the master outlet connector,two pairs of low voltage signal conductors that extend between andelectrically connect the master inlet connector and the master outletconnector for routing temperature signals from the first and secondtemperature sensors from the master outlet connector to the master inletconnector, and (ii) a slave segment that includes a slave outletconnector and a pair of slave AC power conductors that connect the slaveoutlet connector electrically in parallel to the master AC powerconductors; and G. A plurality of T-type slave power cables, each ofwhich includes: (i) slave trunk section, (ii) a slave branch section,(iii) a slave trunk inlet connector on one end of the slave trunksection that is configured physically and electrically to mate with theslave outlet connector of the slave adapter, (iv) a slave trunk outletconnector on the other end of the slave trunk section that is configuredphysically and electrically the same as the slave outlet connector ofthe slave adapter to accommodate daisy chain connection of a pluralityof T-type slave power cables, (v) a pair of slave trunk AC powerconductors that extend between and electrically connect the slave trunkinlet connector to the slave trunk outlet connector to route controlledAC power from the slave trunk inlet connector to the slave trunk outletconnector, and (vi) a slave branch outlet connector that is connectedelectrically in parallel to the slave trunk AC power conductors and isconfigured physically and electrically to mate with the heater inletconnectors to route controlled AC power to the slave heaters.
 24. Theheater control apparatus of claim 23, wherein the base controller moduleincludes a controllable signal switch and the process control circuit isprogrammed to open the signal switch if the temperature sensed by thesecond temperature sensor is not within a preset desired operatingtemperature range.
 25. The heater control apparatus of claim 24,wherein: (i) the signal switch is connected in series to the inletconnector of the heater controller, (ii) the T-type source power cablesalso include signal wires that connect the branch outlet connectors inseries to a signal circuit at a remote monitoring station so thatconnection of the branch outlet connector to the inlet connector of theheater controller connects the signal switch in the heater controller inseries with the signal circuit; and (iii) the linear-type terminatingsource power cable also has signal wires that connect the terminaloutlet connector in series to the signal circuit so that connection ofthe inlet connector of one of the heater controllers to the terminaloutlet connector of the linear-type terminating source power cable alsoconnects the signal switch of that heater controller in series with thesignal circuit.
 26. A method of providing a high-limit thermal safetyshutdown for a heater that is powered by AC power via an AC powercircuit, comprising: positioning a high-limit switch in the AC powercircuit that is capable of turning the AC power to the heater on andoff; and controlling the high-limit switch with a high-limit controlcircuit that is powered by low voltage DC power from a DC power sourceand that is programmed to (i) compare a temperature sensed by atemperature sensor that is positioned in close enough proximity to theheater to sense heat produced by the heater to a preset high temperaturelimit parameter, (ii) cause the high-limit switch to turn off the ACpower to the heater if the temperature sensed by the temperature sensorexceeds the preset high temperature limit, and (iii) cause thehigh-limit switch to turn on the AC power to the heater if the lowvoltage DC power to the high-limit control circuit has been stopped andthen started again and if the temperature sensed by the temperaturesensor does not exceed the preset temperature limit.
 27. A method ofproviding a high-limit thermal safety shutdown for a heater that ispowered by AC power via an AC power circuit, comprising: positioning ahigh-limit switch in the AC power circuit that is capable of turning theAC power to the heater on and off, said high-limit switch including anormally open relay switch that is powered by a coil to close andthereby to turn the AC power on and that opens when the coil is notpowered; and positioning a PTC thermistor in the heater, directingelectric current to flow through the PTC resistor in series with a coilpower circuit so that the coil is powered from current that flowsthrough the PTC thermistor, providing a drain circuit that closes whencurrent stops flowing through the PTC thermistor and that remains closedto drain current away from the coil when current starts flowing againthrough the PTC resistor.
 28. A method of controlling a plurality ofheaters that are powered by AC power from an AC power source to produceheat, comprising: positioning a heater controller adjacent each of theplurality of heaters, with each heater controller having means forturning AC power in an AC power circuit on and off based on comparisonof a sensed heater temperature to an operating temperature set point tocreate AC controlled power, wherein each heater has an inlet connectorfor receiving AC source power into the AC power circuit and an outletconnector for delivering controlled AC power to the heaters; connectingthe heaters electrically to the respective heater controllers via theoutlet connectors of the heater controllers so that the heaters arepowered by the controlled AC power; and connecting the AC power from theAC power source to the plurality of heater controllers via a series ofT-type source power cable sections, each of which has a trunk segmentthat is daisy chain connected to the trunk segment of another one of theT-type source power cables and each of which has a branch segment thatconnects to one of the heater controllers via the inlet connector of theheater controller so that the heater controllers are connectedelectrically in parallel in relation to each other in the AC powercircuit.
 29. A method of controlling a plurality of heaters that arepowered by AC power from an AC power source, comprising: positioning aheater controller adjacent a plurality of heaters, each of which has aheating element and at least one temperature sensor adjacent the heatingelement and a heater inlet connector where power wires connectedelectrically to the heating element and signal wires connectedelectrically to the temperature sensor are terminated, wherein theheater controller includes an inlet connector for receiving AC powerfrom the AC power source, an outlet connector for receiving temperaturesignals from the temperature sensor in the heater and for deliveringcontrolled AC power to the heating element in the heater, and a processcontrol circuit that compares the temperature signals to at least onetemperature set point parameter and turning the AC power to the heateron and off based on the comparison of the temperature signal to the setpoint parameter; operating one of the heaters as a master heater byconnecting both the signal wires and the power wires at the heater inletconnector to the controller outlet connector via respective power andsignal conductors in a slave adapter; and operating at least one more ofthe plurality of heaters as a slave heater by connecting only the powerwires at the heater inlet connector of that heater to the controlleroutlet connector via power conductors in the slave adapter that connectthe heaters electrically in parallel to the AC power.
 30. A method ofcontrolling a heater that has an AC powered heating element and that hasat least one temperature sensor, comprising: connecting a heatercontroller base module electrically to an AC power source and connectingthe heating element and the temperature sensor of the heaterelectrically to the heater controller base module; comparing temperaturesignals from the temperature sensor to a temperature set point parameterin the base module and switching the AC power to the heater on and offin the base module to provide controlled AC power to the heater based onthe comparison of the signals from the temperature sensor to thetemperature set point parameter; and displaying the sensed temperatureand the set point parameter by attaching a detachable expansion moduleto the base module, wherein the expansion module has display apparatusand a microprocessor that is programmed to receive sensed temperatureand set point data from the base module and to process aid sensedtemperature and set point data for display at the expansion module. 31.The method of claim 30, wherein the expansion module also has data inputapparatus for inputting to the microprocessor instructions to adjust theset point, and wherein the microprocessor is programmed to receive andprocess the instructions and to send signals to the base module toadjust the temperature set point according to the instructions.
 32. Themethod of claim 31, wherein the base module also uses adjustablehysteresis and temperature range parameters for turning AC power to theheater on and off, and wherein the expansion module also hascapabilities of receiving and displaying those parameters and ofreceiving and processing adjustment inputs for those parameters andsending signals to adjust one or more of those parameters in the basemodule.
 33. Wire connector apparatus for connecting an outlet connectoron a first component to a inlet connector on a second component,comprising: a latch protrusion the inlet connector; a pivotal latchlever on the outlet connector, said pivotal latch lever having a dog ona distal end of the latch lever that is sized, shaped, and positionedfor engagement with the latch protrusion when the outlet connector ismatingly connected to the inlet connector, and wherein the secondcomponent includes bias apparatus positioned to bear against the distalend of the latch lever in a manner that resists a pivotal movement ofthe latch lever that is required to disengage the dog on the latch leverfrom the latch protrusion in order to disconnect the outlet connectorfrom the inlet connector.
 34. The wire connector apparatus of claim 33,wherein the bias apparatus includes a contilevered biasing tab molded asa part of a housing on the second component adjacent the inletconnector, said biasing tab being yieldably moveable against an elasticbias in response to a pivotal force applied to the latch lever.
 35. Thewire connector apparatus of claim 33, wherein the bias apparatusincludes a spring positioned adjacent the inlet connector.
 36. The wireconnector apparatus of claim 33, wherein the spring is a leaf spring;37. The wire connector apparatus of claim 33, wherein the spring is acoiled compression spring.
 38. The wire connector apparatus of claim 33,wherein the bias apparatus includes a compressible material.